Hey Michael
Enjoy your new gear. I used the Nikon D800 for 4-5 years and loved it underwater. The only pain is housing the Nikkor 16-35. A 230 dome is essential and that's horribly expensive and the devil's own for travelling. I'd suggest sticking with a fisheye: either the Sigma 15mm or the Nikkor 8-15. You can then use a much smaller dome - 8".
On strobes, they and the accompanying arms are one of the few bits of u/w gear that, I think, are worth seeing as a longer-term investment. They will stay with you as you move from system to system through upgrades. So buy well and buy once.
The Inon Z240 was a very popular go-to model for many on Wetpixel. These have now been replaced by the Inon Z330. I had the Z240s for years and thought they were brilliant. I've got no experience of the Z330 but I'm sure they are good. Compact, good price, use AA batteries, sufficient power for all but the widest wide-angle stuff. You may well be able to find a couple secondhand through the Classifieds.
I can also recommend the Retras - Prime or Pro. I've just bought a pair of Primes to replace my Z240s and really like them. Beautifully built, great light quality, more powerful than the Z240 and, for me, work really well with Retra's snoot, the LSD. They are also AA battery powered. The Prime and Pro are pricey but they are quality bits of gear and should last well. All dealings I have had with the company have been first-class.
Hope that helps a bit.