3/16" ID beer line, 10' per line. Star with 10' per line and cut off to increase flow. I usually end up using 7' or 9' depending on the line, they have different resistance by brand.
Some sort of Co2 setup, I recommend a 10-20lb tank as fills are way cheaper per lb with larger tanks. 10-15-20 tanks all have the same footprint, they have different heights. Fire protection shops seem to have the best rates for filling tanks and used cylinder prices.
A decent 2 gauge regulator, or maybe a double regulator depending on your preferences, and some sort of manifold to split the 1 or two pressures you want to use. Some would recommend a bank of secondary regulators to control easch line individually. That would be nice but not necessary. You want shutoffs for each line that have check valves.
You'll probably want a drip tray of some sort. There are some cheap ones and some really overpriced ones. Search this forum, lots of drip tray posts.
Connectors/couplers for the kegs you want to use. There are some cool flared fitting adaptors made to fit the commercial keg couplers in case you plan to buy one occasionally.
External Thermostat - there are a lot of ways to go about this, there have been some honeywells going cheap on ebay, there is the Love controller route, the Ranco digital, and the Johnson Controls. each one has there merits, the next one I buy will be a Ranco, they can be found for about $50. The honeywell and johnson controls units have an analog dial and a capillary thermo probe. The capillary tube is somewhat fragile, and the dials are fairly vague. I have a JC on my keezer and it's working fine. The Love controls look great but need some mounting and they do not come pre wired, although that's pretty easy to do. The JC is the only one that is pre wired.
I think that covers it. A small fan never hurts to keep the air circulated. Don't be tempted to drill the wall of the freezer, bring in everything through the lid or the collar if you make one.