It depends which nation. You would need ALOT of vets, and you probably wouldn't be able to run AA or HH.

You would also have to get engineers with a good repair stat, and not elites.

I've done it with UK, but thats with 200 vet Engies with +10 or better repair, and two +12 300 vet repairmen. I don't use that setup often though (as I like either HH/Pom Pom's, or running a seaman/2 scouts).

As I said earlier, it depends on the nation. Some need more OH time than others, some rely on the repair time more. 

Forget about the SD cap, you reach it at BB3 or BB4.

Normally, with only engineers, even UK ones, you would not reach the repair cap at BB6 (35 million true ability), even if you vet cap them.