I usually recommend 5000km of break in on all the trannies I build with regular Canadian tire gear oil. You will notice the fluid slightly silver from the break in. It's normal, especially with tighter preloads and newer parts. The more you change the oil, the more cleaner it gets.

I wouldn't worry about the 6500 rpm NLTS, just try not to be too aggressive with it. You can obviously use NLTS and shift super slow or just slam it in. I don't even consider that high rpm