The best way to do a compost smaller then 3x3ft would be to make a bokashi bucket and a worm bin. You can even use cockroaches or black soldier flies. But i like my wormsXD a bokashi bucket is a 5gal bucket with holes poked in bottom and a screen to catch solids or smaller holes. Then put it in another solid bucket without holes. Place veggie and fruit scraps (can use little meat if you leave it longer but to be safe dont) in bucket. Cover this with a "bokashi" bran. (This is just LAB sprayed on wheat bran and dried) Then you leave it for around 4 weeks. After its done you take it and bury it in your worm bin and they go nuts. Takes a few months off the composting process. All this stuff can be done inside.
If you want top grade castings dont just use any fruits and veggies. Use certain ones depending on your needs. Personally i use my veggie compost for outdoor gardens and i use special compost for indoor. My compost consists of lots of organic straw, leaves, yarrow, nettle, kelp, neem, barley, alfalfa, good grass, egg shells, osyter sells, several good rock dusts, lots of ferment scraps, kombucha scobys, LAB and the leftover curd.
I have a fun approach to gardening. Something you can get your kids to do for you. And they can eat or drink it if they want. And its healthy for them. Feed it to them every day. And your animals too!
Basicly everything they sell at the hydro store is garbage and i can tell you exactly whats wrong with it and how you can do it better for cheaper. And if i see a friend going to spend money on garbage ill tell it exactly how it is.
Also this is a good easy down to the point place for composting:) http://www.timetorecycle.com/reduce/composting.asp