I enjoy heavy classes.
For open world/fractal/raid? if so:
1) yes, a berserker sett with scholar runes will fit and work for all 3 classes. (you will need to run different food on the 3 though)
2) for raids, yes. Generally all groups run 2 wars, where guard and rev are less used. And more depend on the rest of the group composition. If you are new to raids (I assume you are), then war will prob be the easyest way to get a spot. When you get better a guard is often really good and can do alot for the group. And (atm) rev is kinda niche.
3) condi sett for war is good, for some groups. But it generally take better groups that already know what they are doing. A normal power war is the “safe” pick.