A computer interface (armory, page 82) comes with a t1 computer, Artificial personality and control module. It can activate a single armor system once per turn after a condition is triggered. It can be linked to tools or weapons attached to the armor with-in the limits of a control module. The main gripe is if a GM would let me order the AI to fire as a trigger condition.
The total cost of this set-up (minimum) is: 3450 for battle harness, 6000 for interface, 2400 for tactical energy converter (cheapest explode weapon i could find besides grenade launchers)
Totals: 13,850. Over 80% of a level 6 character's wealth, just over half a level 7 character.
I would only need 2 feats, heavy and power armor. The control module covers proficiency already.
Keep in mind I'd be aiming to have the power armor already for strength, letting me focus on cha, con and something else. The mounted weapon set-up is extra.