What you use as a worm farm can differ on various needs. You mentioned you don't want it to be too big. What will you be composting with your worms and what kind of volume? Weeds? Brush? Kitchen leftovers? Knowing that will help you to know not only what is "too big", but also what would be "big enough".
I have an old bathtub and a couple of 9" x 18" x 36" cement mixing trays. I can compost an awful lot with that space, but currently, I'm rebuilding my worm herd after a significant loss. When my worm populations gets to where it was, I will have many, many hundred thousand worms, and they'll eat it all up in short time. The bathtub came out of a bathroom remodel, and the two cement mixing trays were cheap at the farm supply.
Stacking trays such as used in Can-O-Worms or Worm Factory will save you space, and each tray is about 5-6". With one of those, you can add trays to accommodate whatever you throw at it, as long as you have the worms to keep up. But Both Can-O-Worms & Worm Factory are not cheap, unless you get them second hand.
In either case, once the worms have been at it, they will break it all down to small spaces (the original trash compactors), and you refill and do it again and again, until the bins/trays/whatever fill up. But if you're talking processing all the weeds, dead fruit/veggies/stems from a 1/2 acre garden, you'll want at least a couple of Cans-O-Worms, or Worm Factories. For me, that would mean probably another bathtub to go with what I have to give me very generous room at the end of a summer harvest, but by the time spring comes back around there would be room to do it all over again - assuming you have the worms to care for it.