You already have the hard part. If you want to start slow all you need is a CO2 tank, CO2 regulator, a keg, some disconnects and a pony tap (hand held thumb valve). Then you can enjoy one of your kegged beers while pondering the next step.
But if you want to go all out and serve from 6 taps all at once, you will need the following:
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A wooden coller that fits between the lid & body of the freezer - provides a place to mount your beer faucets. Also, you need the beer shanks & faucets & tap handles.
Or
A nice 6 tap T-tower that you can mount on the lid. You will also need a beer tower cooler to blow cold air into the tower & keep the beer shanks cold.
8 - 10 kegs - you need more than 6 to serve from 6. Probably the best source for used kegs today is
www.kegconnection.com in Texas.
6 disconnect sets
At least 36' of 3/16" beer line & at least 20' of 1/4" CO2 line.
CO2 tank & regulator
Secondary regulator set - because with this many beers you will likely be serving different beers at different pressures. How many secondary regulators you need depends on the number of different pressures you need.
Manifolds or stainless steel Tees to split out the CO2 lines.