Here are some situations you may be involved in:

enemies in a row - first use liara's SINGULARITY or javik's DARK CHANNEL etc. then use SHOCKWAVE to blow em up

enemies around you - nova and jump backwards

far away enemies - passive power(sglrty, dchannel etc) and fucking charge nova charge

in my opinion just one rifle (not exactly a rifle - FALCON with inferno ammo) it's a grenade launcher madafaka anti armour ammo on 50 percent (garrus ) or warp ammo (liara)

Here are some situations you may be involved in:

• Enemies in a row - first use Liara's Singularity or Javik's Dark Channel, then use Shockwave to blow 'em up.

• Enemies around you - Nova and jump backwards.

• Far away enemies - passive power (Singularity, Dark Channel, etc.) then alternate Nova and Charge.

In my opinion, you could use the Falcon with Inferno Ammo (it's like a grenade launcher!), put anti-armour ammo on Garrus or put warp ammo on Liara.