Are you a diver? Captain? Experience on boats? In other tourism industries?
There is a steep learning curve ahead of you. If you intend to employ guides then you can act as a more 'silent' partner and look to organisation of the boat.
BOAT- 'bring on another thousand'. Diving boats are expensive, first to buy, then to run, then to maintain. You can lose big time if you're not boat savvy.
If Fiji is your goal, then go to Fiji and look at the area with critical eyes, talk to people etc. Internet education pales in comparison to actually being there- not just a vacation, but a proper 6-12 month stay.
Diving is a bit like the resaurant/bar industry in that it seems like a good thing to do... until you end up on Ramsey's Nightmares. Unless you have approx $300 000 (not joking) that you can walk away from, I'd be very cautious about entering the diving industry without lots of experience in similar industries.