just the engys.

Boosting sailor make ur life on lower tier bb class easier, at high level it would allow u to 'skeleton' ur BO & main gunner to save weight (for more bulge armor or AA). Engys and reps is a must at first so u can reach 900SD as soon as possible.

Looks like KM crew

I would boost the BO too because when not you wont see your shells land for a long time and that is more then anoying.

If it is a KM crew you do, you can skip your AA gunners and scout if your low on boost.

When you can boost all crew even your scout. All sailors give you Repair and SD.

Ty for your answer guys! and yes, it's a KM crew :)
I'll proceed to boost engys and reps!