Hello there Laiv!
I`m not playing on the P2P Server myself but when I read about it I usually hear like "There´s a handful playing on P2P" So I don´t think there´s too many people left and not sure how it looks with PvP or PvE then

On F2P there are more people quite a lot of guilds who are doing Raids and Dominion.
Class-wise it depends what you´re looking for I`d say. You can change class easily nowadays even on P2P! Summoner, Priest and Warden can Heal (Mainly taken Summy and Priest), for Raids tanks mainly are Warrior and Demo I`d say don´t really see Pally tank. Support classes are Engi, Bard and Warden. Can´t really say much about Paladin since I´m not playing it sorry :/
Hope that helped already a little! If you have any other questions, don´t hesitate to ask!