Hi jchance,
1.- Yes there is a market for Nikonos stuff, price will depend on condition and how rare it is, as always. I have bought some very nice cameras and strobes for very cheap, but I have also seen some very pricey ones being sold on eBay and similar and they sell. Collectors are a very particular breed. Other than me, I have not seen people using Nikonos for the last five years.
2.- I only use Sea and Sea housings, first one for the D100, then one for the D300 and now one for the D800e, but several friends use Ikelite and Aquatica.
Ikelite is less expensive, and lighter (which is nice when you travel and you will save some dollars since you will not have to buy so many floating devices). Aquatica and Sea and Sea seem to be very similar. Metal construction, heavy but very resistant, very well made and ergonomically excellent. Once I saw a guy on a boat, getting out of the water and droping very violently his housing in the fresh water bucket where everybody had our cameras rinsing, one Ikelite got broken from the impact and my friend's Aquatica got scratched. There is something to think about. Also you can use almost any strobe brand available (for what I read Ikelite seems to be very picky in this department).
You will need the housing, the ports (wide and macro) and the extensions for the ports. Aquatica allows you a more wide selection of lenses to use with their housing than Sea and Sea.
As AZTinman mentions reliability depends on you. All brands that you mention are 100% reliable, but every housing will eventually get flooded unless you do not use it, it is like Murphy's Law. They are very well made and IF you follow the right procedure 100% on 100% of your dives they will not fail or flood, but I assume that you are human, so... you know.
I believe that in the end your decision will depend on how much money are you willing to spend, and I assure you it will be A LOT!
3.- Your video light will work fine with any of the brands you mention, probably you will need more lights, but to start it will do. The strobe will work with Sea and Sea housings I do not know with the others, but you will not have the possibility of TTL. That is a very important point, check compatibility with TTL for the housing you select. When I changed to the D800 housing, I found that the housing was not compatiple with the TTL converter which needed to be modified and after that it will only work with only two models of Sea and Sea strobes. Bummer! I can use TTL with the optic fiber cables, but it means slower frame rate, slower recharging camera flash time and higher battery consumption.
Just in case you are unaware, there was a Nikon recall on the SB-103 check it here:
Nikon | News | Notice of Recall Request to NIKONOS Speedlight SB-103 owners
You can use your video light for photography with excellent results for macro, in wide it will not be as good to say the least.
I recommend that you buy your housing used, you will save a lot of money, just send it for service. Backscatter has given me an excellent service, but there should be others as good as they are. There are several forums where you will find what you want with a great saving SB photography forum is probably the best one.
Good luck with your decision.
Ramon