Hello from Raleigh, NC

[davidstcldfl]

1. Would two 55 gal drums be enough for the sump tank and FT?

A drum for your sump would be fine. Just make sure it is clean/safe for the fish.
-advantage...it's sides would be stronger, in regards to being buried
-disadvantage....the depth...now you'll have more 'head' for the pump to deal with.
The sump needs to hold more water then the GB's combined.

Fish tank....you 'could' use a 55 gal drum. The height would seem awkward to me. Plus, now your air pump needs to be able to pump deeper

I would need to buy a new pump since mine is not submersible.

Is it the kind that has a suction side and a discharge side....like a swimming pool pump has....? Run the suction line to the bottom of the sump.

.

Would 330gph, 150" lift, .06hp, 1/2" output pond pump be enough?

It looks like it 'might' work. If you put a drum in the ground, plan on keeping your FT as low as possible. Keep the 'head' as short as you can.
When buying a pump, figure how much water you want to move. Figure out what the 'head'/height you need. Add a little to that for resistance of flow in the pipe. Now, you need to find a 'performance curve chart' and see if the pump will meet your needs.
Here's an example...
http://www.aquaticeco.com/images/static ... es/MD2.gif

Also, look to see the wattage of the pump. In the long run, it would be better to spend a little more, on a more efficient pump.

3. Can I use flexible plastic tubing instead of PVC in some places? Should there be anything special about it?

If you use clear tube, and have water going through it....it will turn green. After your system gets established....all your pipe will have algae growing in them. It's best to slightly oversize the pipe .

It's 3/4" PVC with holes drilled in it and a 90 degree elbow and then a 2-3" piece of PVC to the max water height of the GB.

Most people do not let the top of the gravel get wet. It 'will' start to grow algae