At this point in time there are no Combat NPC’s. This is soemthing we will be working on and will release an initial trainer type NP followed by a slew of mission based NPC’s.
At this point ther eis no pop ups inside the combat screen. But you do level up as normal.
Sure you can purchase items even if you cant use them. You will simply have to hold on to them until you can.
Coops