'Reverse' quarantine

I currently have a 10G tank all happy and cycled, and I'm trying to get a 33G cycled to use as my main tank. I'm not sure that the larger one will ever cycle (I've been feeding it food for 2 weeks now, and I've borrowed gravel from my other tank twice now, without any signs of nitrite) but I'll be optimistic and assume that eventually the thing will cycle.

Once the tank has cycled I'll have two tanks going, so I'll feel reasonably comfortable buying more fish. I could simply take the fish in my current tank and put them into the new tank, however I'm worried about something random being in the tank and killing my buddies.

I was thinking about placing the new fish into the large tank and leaving them in there for 3-4 weeks for observation before combining the two populations. Essentially, I would use the main tank as my QT initially since nothing is living in there anyways. At the absolute worst, I end up having to drain and restart the new tank. Is this really any worse than putting the old fish into the new tank, and then putting the new fish into the old tank? Why?

Are you suggesting putting the old fish and old filter on the new tank without waiting for the new tank to finish its cycle? Presumably this should work okay, since the 10G filter already has enough bacteria to handle the load from my old fish. I imagine the extra volume of water to treat would cause problems, but it would also keep the ammonia/nitrite levels down, so it may very well balance.

This would (hopefully) cycle the tank faster than borrowing gravel, but it doesn't handle the second problem. I'm still worried that I may have not washed something thoroughly and I have some trace badness in the water that's going to make my fish belly-up. I -doubt- that this is the case, but these are the last of my original fish and I really don't want to risk it with them. If anything is going to have to be a guinea pig (and something will since I can't afford to test for -everything-) I'd much rather it be some fish that I haven't gotten attached to.

The tank is new, and while I cleaned it with chlorinated water I gave it a heavy dose of dechlor before I started to cycle, and will be dosing again once things are settled and I do another water change.

There really isn't a rational reason for me to be worried other than my fiancee and I were upset when two of our fish died (the two we named, of course) and I'm paranoid about, perhaps, having bought funky gravel or something off getting into the tank when it was at the store. I can't think of anything that might be wrong (otherwise I would try to solve the problem before putting any fish in the tank) but I'd like to keep the fish we've gotten attached to safe. I'd feel like a complete *** if I killed our established fish. Hence the 'reverse' QT and (hopefully) perfectly safe guinea pigs.