First the fridge.You will need a fridge or converted chest freeze capable of fitting a post mix keg in it, two is better. If more room is required the shelving on the back of the door can be removed and replaced with a piece of ply or similar material. I am lucky and have a fridge that will hold 4 kegs with the shelving in place to hold my glasses.
If using a chest freezer you will need to use an external thermostat so it will operate at the temperature you require about 3-4 deg C.
Selection of Tap or Pluto gun.There are many different types of taps available so some research here is good. Don't rush in and buy the first tap you see, look around. There are taps that have an extension designed to go through the side or door of the fridge, there are taps that screw or snap lock into a fitting and can be adapted to go through the door or side of a fridge, there are taps that are capable of pouring with nitrogen, there are taps that regulate the flow rate of the beer at the tap, you get the picture there are lots of different taps out there. So have a good look around then decide what you need in a tap. Do not just look in the Home Brew Shops though, look for business’s that service hotels/pubs/clubs, if you see a tap you like at you local ask them where they got them or who services their system. Lastly you need to be happy with the look and price of the tap.
There is not as much of a selection in pluto guns but still have a look around as there are different types.I went with snap lock pull down handles as they could be remove from the fridge to stop little hands getting at the beer. They could also be used in a font with future bar expansion. I also got a pluto gun so I could take a keg to parties camping etc.
The rest of what you need.
For the rest of the items you need there is not a lot of differences.
Kegs, ensure they are in good condition and hold pressure. It is worth get a new seal kit with each keg and replacing all the seals. Also check they all have the same type of connections there is two different types pin lock and ball lock, I recommend ball lock as they are the more common. The number of kegs you will need will be determined buy the amount you brew/drink and your budget. You will need at least two at the start.
Regulator, you can get single or dual gauge regulators dual gauge regs show the bottle pressure and keg side pressure, single gauge regs show keg side pressure only. Both work well in a keg set up. If you are going to run multiply kegs at once you may want to considerer a dual gauge dual pressure regulator this will let you have two kegs at different pressures.
Line, you will need beer and gas line. Gas line is 5mm inner diameter and 8mm outer diameter. Beer line is 4mm inner diameter or 5mm inner diameter. The important thing with the beer line is to get the length right; the rule of thumb is 2 meters long for 4mm line and 3 meters long for 5mm line.
Last you will need beer and gas quick connects and line clamps.
Putting it all together
Now you have all the bits it is time to put it together.
Drilling holes for the tap fitting in the fridge/freezer, if you have decided on taps you will need to drill some holes in the fridge/freezer. Measure were you want to put the taps (this can be in the door or in the side of the fridge) checking the inside of the fridge as well as the out side. It is best if the taps can be installed higher than the top of the keg so place the kegs in the fridge/freeze and see were they come to, also on the out side if it is a two door fridge you still want to be able to open both doors while the tap is installed. So measure measure measure.
Once you have worked out where you want to place the tap/s you need to check that there is no wires or pipes hidden in the door/side you want to drill in. To check this if it is the door you can remove the back and have a look, if it is the side feel the outside if it is warmer than the rest this is a sign there is pipes in that wall. Once you are happy you are not going to hit any pipes or wires and your measurements are correct you are ready to drill. Make sure the fridge/freezer is turned off and unplugged. Next use a punch to mark were you are going to drill. Drill a very small 1-2mm pilot hole through the metal skin of the fridge/freezer only. Then get a skewer and poke around in the insulation through your pilot hole feeling for any pipes or wires you may have missed. Once you are happy you are not gong to hit anything increase the size of the pilot hole in the metal skin only and have another poke around. You should now be happy to drill the hole right through at the size you require to fit your tap fitting.
Put the tap fitting together in the hole. If you have a tap similar to mine the tap fitting will be made up of several bits. I have a nut and tail, panel adaptor, female snap lock connector, and the tap. Place some glad wrap or other covering over the back of the tap fitting to stop any insulation getting in the fitting when pushing it through the hole. Tighten the fitting to the point were it is held firm in place but is not crushing the door. You can use a small piece of PVC pipe if desired, drill your hole to the diameter of the PVC pipe place this in the door trim to the correct length then insert the tap fitting in the PVC pipe this will stop the insulation getting in the tap fitting if you do not cover it and you crushing the door. This is not necessary but some people do it.
Drilling a hole for the gas line, if the gas bottle is going to be outside the fridge (gives more room for kegs). Again measure measure measure. Be aware of the same things already mentioned above and use the same process for drilling the hole once decided where it will be. The size of this hole will be decided by what type of connectors you have and if you want to be able to remove the gas line from the fridge. If you have snap lock like gas line connector or you do not intend to remove the gas line from the fridge you can drill a small hole the size of the line. If you do not have these types of connectors and will want to remove the line from the fridge you will need a larger hole that lets you get the gas quick connect out. I run the gas line into the fridge via a large piece of tubing so the sharp edges of the hole do not damage the gas line.Connecting all the lines. The most important thing here is the length of the beer line. The beer line as well as getting beer to the tap is required to reduce the flow rate of the beer to the desired rate so it will pour correctly. If your line is to short it will not provide enough resistance to the beer as it rushers to your tap resulting in a glass full of foam. So you need to now the inner diameter of the beer line this should be written on the line. If you have 4mm beer line you will need it to be about 2 meters long from the beer quick connect to the tap or pluto gun. If you have 5mm beer line you will need 3 meters from beer quick connect to the tap. These lengths will enable you to get a good pour at a pressure of 70 - 100 kpa. The length of the gas line is not critical as long as it reachers from the gas bottle to the kegs.
Once you have the line cut to lengths you need to connect it to the beer (black) and gas (grey) quick connect fittings. To do this heat the line with some boiling water from the kettle and force over the barb on the quick connect. This can be very hard especially if you are using 4mm beer line. I found using a plastic chop stick to stretch the line helped to get the connectors on. Once the quick connects are on the line you need to clamp them.
Now connect the other end of the beer line to the back of the tap. Push the gas line through the hole for it and connect it to the regulator.Now are ready to connect the quick connects to a keg and flush some Keg and Line cleaner thought the system to give it a clean. Then fill a keg with beer gas and drink.
Additions
You may wish to build on your system buy adding additional taps. To do this you will need to split the gas line. This can be done with a simple T, a dual gauge dual pressure regulator or a gas manifold.
I use a simple T to do this and it services my purpose. The T I use though is not clamped, it is John Guest connector that can be removed.