If I could thumbs-up/rep posts here, yours would be getting major karma right now. Thanks so much for taking the time to type all this out. It's really helpful/clarifying. As a noob, I'm prepared for a bit of steep learning curve for this sort of game, but this really does help out a lot.
Thanks to the others who took time to post (much-needed!) advice too.
I'm in two minds about joining groups right now. Mainly 'cos it's not really something I'm used to, wasn't planning on doing, and I don't want to ruin someone's else's game. I'm going to see if I can get a bit better first, before weighing someone's group down with my lack of skill.
Solo questing will do me fine, at least for now, so all the various tips above about how to spec for this are even more helpful/relevant.