If you go with the smaller, liner pond, then definitely do a bottom drain. I've got a 15'x7'x3-4' deep liner pond (3,500g) and I wish I'd put in a bottom drain. The skimmer works great collecting off the surface, but I don't have nearly enough flow along the bottom of the pond. The gar I have out there love the slow flow water, but its not so great for filtering and general cleanliness of the bottom.
If I had it to do over again, I'd do a bottom drain plus a skimmer, with separate pumps for each, and separate returns for each.