1+2) Jedi Shadow (55), Jedi Guardian (55), Vanguard (55), Sniper (55) (but i think it didnt work for all of my character)
3) Shadow max affection; Guardian ~4-5k affection; Vanguard ~3-4k; Sniper ~5k affection
4) I bought with my Shadow for 1million credits in the legacy vendor and then i unlocked her in the collection for 700CC
5) no absolutely not (only the first conversation achieved with my characters ...)