Where is a good 'before I play' guide or beginners tips? Even just a "this is vaguely how each class plays"
The other thing is like is there a relatively spoiler free guide of "don't be dumb at the game" for instance like with some RPGs the first thing I've done is jump in and then buy heaps of shit at every town, and vendor shit when actually you should wait for drops and disenchant! But in others it's different... more like don't let me waste my time guides.
I'm overthinking it but whatever.
The OT will probably have some info. There's a very detailed wiki that has a lot of info too. I can't really think of some crazy "don't do that or else" situations in this. Do carry oil flasks for your lantern as it sucks when you run out of oil in the middle of the night/down a dungeon, but just one is generally enough and you can get by without it anyway.
There's gear in chests and stuff but it's not the main source of equipement, buying stuff from the vendors is how you gear up, and then you sell stuff back, there's no reason to keep gear(other than stuff that can be used by other classes then you can keep them in your "bank" to equip if you switch classes, although it might be outdated at that point and you could find better stuff on the vendors).
I guess one thing is you'll come across some Portcrystals in the game, you have to drop them in the world to create fast travel points. Generally speaking, you'll want to drop one in every place you get one, as you'll probably have to come back at some point later on for sidequests, and they're generally given in places that are far from cities. So when you get one, walk out of the dungeon you're in at the end and drop it outside. It'll save you 5-10mins the next time you have to run there.