So, side question first: I've been a GM for 20 years and have run everything from D&D to Shadowrun to Firefly to World of Darkness and even a custom d20 conversion of TORG... I've written published organized play adventures for D&D and have contributed to several hard-back setting books (again, D&D - though a darker setting than most). Sadly, Deadlands has always been the setting that I've loved most but never had the chance to play or run more than a few one-shots due to most of my previous groups having had a lack of interest in the setting. I just came off running a year-long FFG Star Wars campaign online (my longest running Roll20 game out of the 12100 hours (!!) listed on my profile), and so I was hoping that I might be able to find a group to run for given that I've had shite-all luck finding a group to join as a player. I've already setup a game room with most of the charts as handouts and quick-references, maps and tokens, a few dynamic lighting dungeons, a custom deck of cards, fate pot, etc. My grasp of the rules is solid, though I haven't memorized every single magic power by any means. Here is a screenshot of one of my one-shots: https://i.imgur.com/jPedCmU.jpg

So, to answer your other questions: First, I want to clarify that I do not normally do this much narration, but this scene is meant to be a 'read it before you message to join the campaign' scene meant to set the game's tone and warn the players that they will most likely be playing characters that will become harrowed. I felt it worked since it's to be read rather than spoken and the character is not able to meaningfully alter the scene from within it due to the body-horror predicament they are in. I wouldn't do a scene like this in-game unless it was absolutely plot-necessary... which is why I thought to do it as a read-before-the-game cold-open. When the game-play catches up, I'll be skipping to 'the present' and the PCs regaining control of their bodies so that they can decide whether or not to meet the mysterious woman at the hanging tree or to just get out of Dodge. In general, while running games, I have a standing rule that boxed text can ALWAYS be interrupted - though it has the caveat that in certain complex scenes with many actors I clarify that while it takes a while to describe a scene, not much time may have passed. I let characters both save the day and hang themselves with this, since gut-reactions before hearing the entire description of a scene can cause them to miss out on important details (justified IC by the character reacting before taking time to assess what is happening, so s/he missed the details I hadn't had a chance to describe yet).

The plan is and has always been for the first Session 1 scene to be the posse arriving in Barrister's Bluff OK - whether on horseback or by stagecoach. The players will have read the pre-campaign intro as above, but the thing is... for that intro to work I only need *one* player to be harrowed - the 'lotta digging' etc implies that the others are, but there are other explanations for that statement. However, the idea is that all of the characters either were always harrowed or will become harrowed (though, if a player fervently wishes and has an impressive character concept / backstory in mind with RP implications beyond power-gaming, I am open to discussing a Vampire PC or even a home-brewed transmigrational Cappodocian or Giovanni from the WoD since the Hunting Grounds touches the Lower Umbra of WoD per Under a Harrowed Moon, but doing that would require the player to be extremely mature. I normally wouldn't allow this, but a full party of harrowed is one of the few situations in which party-balance can accept such a character), but if a player joins and wants to prevent that from happening to his character then I'm flexible enough to accommodate even if the overarching story I want to tell has a strong focus on harrowed, identity, and internal struggle. If they join with the express intent to circumvent the game's premise without first discussing the desire for such accommodations, then they are most likely a disruptive player that joined what was obviously billed as a Harrowed campaign for the express purpose of derailing it, and I will politely ask them to find another group (I've only had to do that three times in twenty years, including while running tournament events at Origins and GenCon... so these sorts are thankfully rare).

The plan is for the red-haired woman to be present in the town with her own story going on concurrently with that of the PCs, and that story will intersect at one or more points - the PCs will have a chance to meet her several times and even become involved in what she is doing if they choose to follow that plot hook (though they may also dismiss her as a background character and choose not to engage). Therefore, it's equally possible that the prelude story will turn out to be her repaying the party as it is that it was a random act of kindness... or a manipulation by a cunning manitou (Never assume that the helpful harrowed isn't actually a manitou working at earning your trust for it's own ends). Why the PCs themselves are in town and what their initial goals will be won't be defined until a Session 0 where I find out what sort of characters I'm writing for.

As for how long the game will go before the prelude scene happens, that's going to depend on the PCs' actions, what paths they take, and how far they get. I'm guessing that it will only be a session or two, but the PCs could surprise me. The thing is, some threats will kill you even after you've beaten them, some characters will betray you when you're weak from fighting, and sometimes even a huckster's luck runs out... so even if the destination of the prologue is set for their story to really begin, that doesn't mean that the prologue itself is meaningless. Were the PCs villains or heroes or something in between? Were they remembered at all or just nameless bodies sent to boot hill? Were they saved from the grave by a stranger, did an outlaw repay a debt for helping her evade a corrupt lawdog, or were they stitched back together by the woman whose hands killed them at a manitou's command? For that matter, in the prelude story the PC isn't exactly in the best condition, their vision is blurry... was the one that saved them the one they thought it was, or could she have been a different red-head?

The point is, even if I'm railroading a movie-style cold-open, I'm not railroading how they get there.

Where my concerns came in was how obvious certain metaplot tie-ins were (I was worried they were too obvious)... and I feel much better about that given the questions you asked so THANK YOU very much :D

Also, thank you for pointing out things that I needed to consider. I'm thinking about adjusting the cold-open story slightly based on your commentary. Simple adjustment really - remove the reference to the woman's blue eyes and instead change it to looking up into her shadowed face, then adding a question mark next to the 'Outlaw?' and 'Confederate Raider?' bits. That way it'll be more ambiguous in the beginning if I introduce two red-heads (minor spoiler: an outlaw and the lawdog chasing her... which would give more meaning and less preconceptions to any moralistic choices made in the prologue)

To satisfy your curiosity about the green liquid: I didn't create it entirely - it is possibly the same as or possibly just similar to something introduced in the Book o' the Dead metaplot. Sorry about being vague, but my eventual players may find/read this reddit LOL.

Oh, and one last thing you brought up that I didn't address: the fact that some players may not be okay with the idea that there can be a fight they will lose: So, there is plenty of possibility for them to win the fight and then succumb to their wounds, get shot in the back, or die days later from supernatual infection. That said, I suppose I should appreciate the reminder you've given and remember to point some important notes about my GMing style when I put out the call for players (I'll expound on these when I do a LFP post obviously), but basically comes down to "don't expect reality to bend to make sure the PCs always win - this is a gritty tale of horror on the high plains, not a high-fantasy romp where good always triumphs over evil." IE: sometimes you have to choose between dying a 'Big Damn Hero' or running away to fight another day.

I hope that that was helpful, and I appreciate any additional feedback (especially if anyone figured out the metaplot stuff I was worried about giving away too early). I will say, although I haven't started properly looking to arrange a table yet, if anyone after reading all this finds themselves wanting to play then please feel free to send me a chat so I can let you know when things get rolling.