Thats a fine setup.
1 Thing you should change if you can:
better use gunners with high reload stat instead of ones with high acc. (btw SN has just 1 sort of gunners, so only base can make a difference)
I would change 1 engi for a additional rep but that only if you dont want to overvet them. If you overvet your reps, 3 are fine.
Other possible setups:
-switch 1 Engi for a 2nd scout (usefull for 1on1 or 2on2 battles)
-switch 2 Engis for 2 additional gunners to use AA (RM AA is good range, great damage, medium-slow reload)