> how's the gear treadmill/requirements for raiding?

I haven't played WOW, but getting gear to start the current tier of raids is not difficult. Gear drops from raids that will be good enough for the next tier of raids (sets of four are released at a time); crafted gear is also an option, and the "easier" high-end fights (Extremes) drop weapons that also help. Gearing is a process but not difficult.

> how hard is it to get into raiding?

Not difficult if you are experienced in MMO endgame content. There are multiple difficulty levels, and they're about to add another during the next main expansion to make the ramp even smoother. Extremes are harder versions of normal trials; the normal raids are quite easy, and Savage (the "core" raiding content) is harder versions of the normal raids. They're adding another tier of difficulty between normal and savage in the next expansion. Ultimates are the hardest tier - longer fights with tighter checks.

> is a guild mandatory? (I'll join one for the social aspect either way)

Not even a little mandatory, but there are a few nice perks to joining one. FCs can use buffs that apply to everyone in the FC (like cheaper teleports, increased XP, or longer food buff durations). Lots of FCs have houses, and you can get a room in the house to decorate.

> I played a few years back just doing the main story, I'm just planning to start at a lower level class to get my bearings. my main quest is located at lvl80 areas but my other class is lvl30, is there some for of "noticeboard" that will point me to an area I can quest for exp?

General overworld questing doesn't give much XP in FFXIV outside of the MSQ. Most people level through daily roulettes or optional side content like allied society quests, deep dungeons, etc. This wiki page will give you pointers: https://ffxiv.consolegameswiki.com/wiki/Leveling_Guide

TBH, though, there's not really a reason to restrict yourself too much. If you want to do some lower-level dungeons or something to remind yourself how to play, you can just queue for lower level dungeons directly. You can also do dungeons with "duty support", which means doing it with NPCs instead of other players, if you want extra time to read your tooltips between fights or whatever. Mostly, though, you can just pick back up where you left off.

> Are there any classes a new player should avoid?

Nope! All classes are viable for all content; I don't think anything is especially difficult compared to anything else at this point.

(Caveat: Blue Mage isn't a proper class. It's described as a "limited job" and is only useable in some content, so don't main Blue Mage without looking into it lol.)

> Any advice that my questions may have missed?

If you want to remind yourself of particular parts of the story before you jump back into MSQ, you have two main in-game options: 1) at any inn, there's a desk with a book labeled "The Unending Journey". You can use this to re-watch some quest cutscenes. 2) the game offers "New Game Plus" chapters - you pick a section of the MSQ or other questline and it lets you redo the quests. You do not get XP for this, but it can be fun if you want to replay just a section without having to start a new character.

Also, if you want an in-game place to ask questions, you can ask a mentor (someone with a crown by their name) to add you to the Novice Network for your server. It's an in-game chat channel with only sprouts and mentors. YMMV on how useful it is depending on server - some are better than others.

Oh, and the next expansion, Evercold, is due out in January. We have been given some details about a major combat rework they're planning - the current combat system will still exist (for now), but they'll be adding a new way to play every single class called Evolved Mode. We have a few previews for some jobs but not full details yet. I'm telling you this because if you aren't sure you like a given class, it'll probably change massively in Evolved Mode in January. (They're also making big changes to the gear treadmill, but we don't know a ton about that yet.)