First of all a DIY set up (sugar / yeast) is not insufficiently "sized" for a a 55gal. I did it years ago for a low tech set up. The issue with any DIY set up is inconsistent flow of CO2 which makes dissolution more difficult and can lead to algae issues. Perform a few searches on this forum for CO2 set ups for a 55gal, DIY, pressurized, paint ball, fire extinguisher, etc.
Look into the paintball gun CO2 set ups I hear they work really well and are really cheap. If you wish to go pressurized, which I highly recommend then you should not cut yourself short of the regulator as that's key to success.