Thanks for the comments, and compliments After building the tank out, we found it to be quite deep, and hard to work on. So we built a step to use outside of the tank, to raise ourselves up a bit so its easier to bend over. This helped quite a bit, and since most of the tank will be covered/dark 95% of the time, we didnt forsee a big problem as far as maintenence goes. Hopefully, if anything organic makes it to the sand bed, it'll get eaten by the trillions of bugs/worms/goodies which will be in the sand. If we drop some tools, we've planned to have one of those "pole claw" things that should allow us to grab most anything from the back side of the tank.
As far as pumps go. We looked into an amp master 3000 for the return, and actually decided on a submersible pump for a few reasons. First, we had a spare mag36 laying around with which to test the setup, Second, heating this thing is going to be a constant problem, so actually the waste heat from the submersible pump is actually desirable at this point. Kind of killing two birds with one stone. The head on the pump will be about 10' , at which the mag is flowing around 2400gph. We were shooting for 600gph through both tanks, so its going to be really close with the pipe friction and elbows. If we find that the mag just cant hack it, we'l go out and pay for the larger external pump.
With regards to cutting holes in the tank or lining the tank with epoxy/fiber. This added to the complexity and cost a great deal. Our original though was to go with a plywood tank style sump where there is no liner, but instead use the binary epoxy to seal the wood. We simply werent comfortable with that setup. If there is a leak, we will have the ma36 setup so that we can drain the entire tank in about 10 minutes, even less with us bucket bailing. The computers will actually get moved in the not too distant future, and the washer and dryer will be behind a 12" water break that we will be installing over the next few weeks.