You can make a fuge out of any size tank you want. Of course bigger is better...
For substrate you want a fine sand bed, as well as some substrate that will release a steady supply of iron into the water. Something like fluorite or laterlite will do that job. You can purchase either one from most pet stores (online or a LFS) for a pretty small fee. They are both made for planted tanks.
As for setting up your fuge, you might want to consider ordering the 9 for $99 kit from
www.ipsf.com You can get a large variety of snails, hermits, worms, and macroalgaes for your tank.
For water movement throughout the tank, you will want about 3x to 5x the tank volume per hour. Meaning a 50 gallon tank should be getting 150-250 GPH.