Hello and welcome back,
1) Since the server consolidations, there is very little choice of servers. All should be fairly well balanced within each 'type' (ie, all PvP servers should be about the same). If you plan on restarting however, it may just be easier to roll on a new server in which case, why not. You can check out detailed stats for each server here:
2) Population seems to have levelled out now that we are well into f2p. I normally see between 200 and 250 on the fleet, with up to 80 on each planet. I believe that instance size has recently been decreased so they don't look crowded, but there will be differences between servers.
3) I don't play many flashpoints so normally end up in the 'noob' category there as well (even if I do have 3 post 50 alts!) and don't see people quitting too often. It's never happened from not skipping conversations, although later bosses can prove frustrating for experienced players. Personally I'd suggest that, if you do find yourself struggling with combat, wait until you're slightly over level for a flashpoint before you play through it. The XP grant will be a little lower, but you'll go in that much more powerful.
4) Assuming you know about ROTHC and the game updates, not a lot. I'd look at the update pages for more details but I can't immediately think of anything that won't be there.
5) Yes. They have said that the class stories will be expanded upon, but I don't know when. The Cathar didn't appear for a VERY long time after they were announced, and the SSSP (Super Secret Space Project) is apparently 'progressing'. So yes, they will be continued, but probably not for a while.
6) Three words. It makes money. Since going free to play, the game's revenues have supposedly doubled. EA of all companies won't drop a game that is bringing in money, so as far as I can predict, it should stick around for a while.
Hope this helps.