New player with a few questions.

[Taika]

Hello and welcome to the game!

Since you're Arcanist and level 30+, you should go for either Summoner (damage dealer) or Scholar (healer). You can unlock them both at level 30. You need level 15 Conjurer to unlock Scholar and level 15 Thaumaturge to unlock Summoner. Both unlock quests start from the Arcanists' guild. The cross-class skills you need depends on which one you're going for. Summoner needs at least Raging Strikes (Archer level 4), Quelling Strikes (Archer level 34, don't necessarily need right away), and Swiftcast (Thaumaturge level 26). Scholar needs Swiftcast (Thaumaturge level 26), Aero (Conjurer level 4), Cleric Stance (Conjurer level 6), Protect (Conjurer level 8), and Stoneskin (Conjurer level 34).

Using Aetherflow becomes clearer when you get higher level and get more abilities to use the stacks on. The basic advice is, you should use it whenever it becomes available, so use your stacks before that (if there's something useful to use them on, if not, don't worry about it).

Please note that Virus doesn't do any damage but instead it lowers the damage of the enemy you're using it on, and it also adds an immunity to Virus for 60 seconds on the target you use it on. When you reach higher levels, you may want to leave its use for the Scholar in the group.