A tiny yet really significant buff that will make Engineers viable against (other) infantry.

Make Engineer turrets (AP, AV) able to turn 360 degrees when placed.
You are welcome.

I'm gana have to disagree with this. The MANA is an incredibly powerful point hold option when used correctly. A kitted engi with the right implants is incredibly difficult to dismount from his turret as is effectively requiring to be sniped off, and if they're running Jocky you wont even kill them, just get them to move off the turret until they heal/regen.

If anything, I'd say that at most the turret should be able to be picked up and moved, because sometimes in the rush and frenzy of battle one can place it poorly. The limited arc is about the only disadvantage it has, and if you removed that, you'd also have to remove the shielding it has to compensate. At that point, you basically just have a stationary Heavy Assault with a heat mechanic instead of ammo.

Let go of turret, use primary gun, be as effective as normal infantry.
Bonus points for moving behind turret when flanked outside of it's field of fire to use it for cover.