1) The less chosen classes are paladin, temple knight, plains walker, abbys walker, and some summoner classes (i think phantom summoners)
2) In high lvls Active supports i would say. In low and mid lvls, partys are looking for tanks / bards all the time in party matching
3) Prophet. According to some statistics given by gm some months ago, it is the most popular class. But most of them are boxes. It is very probable that at least one of the members in a common random party ll have a pp or another buffer outside of party for buffs.
Yes. it is posible until certain lvl (like 67,68). After that there arent random parties. Ppl already choose a clan with their own ppl to play with cause spots are dominated by sides
4) It is changing. Many old ppl left. some are returning back, and new ppl is coming too