Kittens and Castle are probably the two largest casual levelling guilds, although there are a ton of smaller ones (and of course I'm biased
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Best place to start looking is here:
http://wiki.project1999.com/Getting_Started
And race/class really depends on your playstyle. I exclusively solo so all my toons are soloable characters (don't look at the ranger!). The 'good' aligned characters are generally easier to play as you can bank/sell at more places, but the evil classes aren't really that much harder (except maybe Iksars).
Welcome aboard!
edit: if interested in Castle just do a /who all castle and ask anyone if an officer is available. I assume you could do the same for Kittens who say Meow but I can't speak for them!
edit2: that link above is about installing client, I was thinking it was more getting started. not to worry, there's plenty of guides here (
http://wiki.project1999.com/Players:Adventure) and the first couple are for EQ newbies.