In single player I maxed Nova, Biotic Charge, Pull, the stat increases, and took Warp Ammo. Didn't bother with incendiary or cryo ammo, and put only a few in shockwave.
For weapons I took the Mattock (with the sight and bonus damage), and the Disciple (bonus damage and piercing). At level five for both I had a recharge of 144%. Switched teammates a lot, but I nearly always had either Javik or Liara for the 'splosions.
Armor was whatever increased weapon damage. Didn't wear a helmet.