Support under the glass is not needed, as it will not be touching wood anyways. If It does, you have a big problem on your hands
If all you have is a 2x4 frame, or plywood base, as long as the supporting members are strong enough to hold the weight, you should be fine. That lip around the tank is there to keep the fish tank strong and to ensure that the bare glass doesn't rest on an uneven surface... as would make it crack.
Some stands have a full-on covered "top" or base, some don't... important part is that as long as you support all 4 edges of the tank EVENLY and it's solid, that's all you need.