I'd say you're golden. Unless the net pots you have don't have very much in the way of holes you should be able to grow decently-sized plants in them. The purpose of the cup and substrate in DWC is just to hold the plant up properly. If they're sturdy enough to support the weight that's all that matters. The other concern is having enough room for the roots to get through.

Ought to be fine.

FYI, if you want to go bigger the lids of most 3.5 gallon buckets fit onto 5 gallon buckets. Transfer the bubbler hardware from one to the other, pop the lid on, and you're good to go without even taking the net pot out of the lid.

Come to think of it, that's not a bad way to go if you want to limit the amount of solution you have to mix up each week. You could upgrade to the 5 gallon buckets when you need them, but not until then.

Interesting.