You mostly need ads mode for squishy solo targets like specials and gunners. If you utilize ads and burst modes well than bolter is pretty ammo efficient. Burst fire is also pretty accurate.
Not with vet feats.
On t5 ~ 2 crushers easly, 3 if good conditions, with bulwarks can be tricky, but again there is enough damage for 3 bulwarks/crushers. With good headshots and lucky crits probably 4. (t3 blessings)