You can use your SB105's, but not in TTL.
Aquatica has a D100 housing. A D70 housing is in the works, but won't be available until August at the earliest.
They will be working on TTL capability (compatibility with Nikon's iTTL). There is no definitive time table. When it does arrive, it will be the D70's iTTL first as opposed to the dTTL of the D100.
Shooting manual strobe power with digital isn't a big problem. Just shoot, adjust and shoot until you get it right. After a while, you will get good at guessing the proper strobe setting and aperture and need fewer adjustments.
If you are within a 1/2 stop or so, you can use software to correct the exposure.
You could always use guide numbers if you want.
I wish I had TTL, but the other advantages of digital are too great to worry about it.