if planning to use AA(reccomended) 5Engine and 3Repair
If not using AA(why idk?) 6Engine and 4Repair
for main gunners you dont really need elites, as they will hit both caps by BB4 if BVE and decent bases.
For DP gunners +12reload or elite reload, class as armament and dont class again until you get to the yamato and want to use them. You can use them for HH classed as armament only :) so they are not just dead weight.
Elite repair are nice to use as you will be running DP gunners and wont have the addtional rep/engine you would have otherwise.
Elite Engineer's are good engies, but only have +9 repair base. You may be better off buying/rolling +12 engines with +10/+11 repair base.
Elite repair as your BO? Even BVE you may not see your shells land for a long time, and the sightlines may never grow to equal your range. But this I do not know...someone else may chime in here who does know.
Elite repair as a scout classed normally would only provide a very small benefit in your repair rate. I dont think this would offset the dissadvantage of having a +9 scout.
I myself delay classed a 12air/11rep MN scout until he was BB4 level as an experiment, and a good stiff breeze would knock him out of the sky :) BVE with 200 vets and now he does ok at BB5 level and adds a modest amount of repair. I'm not sure if he will ever be immune to the best AAW though, So I cannot reccomend this either.
Others may jump in here with tips as well, but dont forget to Search this IJN section for BB crew advice