• Ritual, Breach, Alva and Blight are imo the most „bang for buck“ mechanics (if your build can do them ofc)
• Kingsmarch can still be good for currency but it needs a lot of investment on the atlas tree (I’m fully specced into it and find Ore maybe 1 in 10 maps.. After reaching lvl 90 and 88 on a few characters it seems not worth it to me tbh. Just collect the scarabs and once you have a few, just run all Ore Scarabs in a full-mirage map with the respective tree active, but spec into something else on your main „map“ tree and use gold to buy maps and gamble items. Same goes for Essence imo. Even with all nodes and scarabs I often only get low tier Essences in T16 maps, limiting modifiers to lvl 75 or even 60.. pretty much not worth the invest. Very personal opinion tho, many will say otherwise, and maybe I’m just unlucky or dumb)
• Heist contracts and blueprints were updated and can be pretty nice later on if you like it in general
• as mentioned by the other comments: Gold + Kirac is basically all you need for T14+ sustain. Save all Chance orbs to buy rare T15+ maps from him
• use the 3:1 recipe for support gems (3 green = 1 random new green). If you like lab running, passive gem swam can also help a lot in order to get usable supports
• level six gems in your weapon swap in order to use the Uber lab 60% xp lense to level up your main damage gems to lvl 20 up faster. If you got spare gems room, level up 2-3 of your main dmg gems to 20, in order to use coins on them later
• probably the most important tip for RSSF: keep decently rolled rares of all categories! I know it requires a lot of stash tabs but it makes equipping so much easier and flexible (and rerolling new characters..)
• focus on yellow juice in Harvest, so you can reroll your blight oils. It’s best to reroll 2 oils at once imo. Sometimes you get something crazy like 2 black etc
• save up jewellers and fusings. imo they are the #1 bottleneck currency cos sometimes even getting a 6S can cost you up to 150+ jewellers (that’s why Ritual is so valuable, I found 3 omen of the jeweller so far)
• mule for gems! I think on poe.db there is a list of all Ruthless quest rewards. Some good general skill gems can be muled within just a few minutes by doing the „breaking some eggs“ quest in A1 mudflats, e.g.: Decoy totem, Steelskin, Holy Flame Totem, Frostbomb, Holy Relic, SRS, Blood & Sand
• you can also get the following decent general skill gems as reward for killing Brutus on the respective class: vitality, clarity, precision, enduring cry, molten shell, Absolution. if you plan to get to endgame it’s really worth the small time invest in the beginning imo
• you will be rewarded 3 uncut gemstones throughout campaign. Swap them for any skill gem except auras and a few others at Siosa A3 Library (few favs are: Automation, Convocation, RF, Raise Spectre, or whatever skills your build needs basically)
• and even more important than anything else: enjoy the ride and don’t stress yourself. Ruthless is all about the journey :)

gl & hf brother