I know this is a really old post, but I love to answer questions, what can I say? =)
About LJ Etiquette: -If I've just friended someone, I won't comment about their personal lives. I think I would want to read more of their posts and comment on general entries before I feel comfortable commenting about personal stuff.
-I friend people without asking all the time! I hope that's not weird....
-I do get nervous about posting to a community without being invited to do it. In fact, I don't think I've ever posted to the communities I'm a part of. I only would if I thought I had something to contribute.
-I rec people without asking. I think writers are flattered by it.
-I have never had a paid account, so I don't really know. I'm happy with my Plus Account though. =)
-I think that I would feel awkward replying on the LJ of someone I haven't friended. Also, if I don't know someone that well on LJ, I like to read more of their blog before I comment. But I feel like I can get to know people pretty quickly in LJ... or at least know if I like them or not. =)