It depends on how many vets you are willing to burn for your crew.

If each of your support crew has 40% vets, then 8 late-classed engies and 2 late-classed gunners will give you repair cap. You can save the rest 2 slots for AA/HH or skeleton crew to maximize your armor, as explained in this thread:
http://fm.en.kupaisky.com/Community/Forum/View.aspx?num=18497&searchtype=0&pagecount=0&searchvalue=&sort=5&category=A02&page1=1


If you only want to put 109 vets for each of your crew, then I'd think 6 on-time classed engies and 4 on-time classed repairers will reach repair cap eventually.


If you want to put 200-ish vets for each of your crew, then I'd suggest you use 8 late-classed engies (don't class as engie until Lv 65-ish) and 2 on-time classed repairers.