I like big fish/exotics, as much or more than most... Not tryin to harp on you, but (well I guess I am, I used "but") I hope your planning on a tank at least 10 times the size as you current setup (and I still think that would be undersized!) if you plan on putting a dog shark or a giant pacific octopuss in your tank...
I dont have black tip reef sharks or bonnet heads because I had to sell my 7500gallon shark tank while I was sick, I could put them in a 1000gallon tank but I wouldnt want to because I think it would be undersized... mabey 1-2 sharks in a 4000+gallon but thats pushing it...
Personally I dont agree at all with keeping them for awhile in captivity and releasing them in the wild when they get too big, whatever it is, will be at a huge disadvantage when released, weaker than its competition, not as skilled at hunting, not as immune to parasites,bacteria/disease..... the list goes on!!!!!!!!!!! Also Im not sure that we have any laws against harvesting live marine specimins, but I know it is illegal to do so with any species classified as "game" species(unless you have the appropiate fishing liscense). You may have checked already, just giving you a heads up.
Please dont do it...."the big stuff I mentioned"
Best of luck with appropiate species!!!!!!!!
Cheers