TL:DR answer: Get 6-10 feet of 3/16 line for each tap, and just serve at one pressure. Most beer styles have a range of carbonation level, and unless you are going for perfection, it will work fine for you. I only have two pressures in my 6 tap kegarator, one for most beers and one slightly higher for wheats / Belgians / etc.
Long answer: First, you need to decide what volume of CO2 you want in a particular keg. Once you know that, you can determine the pressure and line length. You'll find it's a whole lot easier to pick an average and work with that, otherwise you'll be changing line length for every beer style, and that will get annoying.
Choose a temperature you wish to serve at, then choose a volume of CO2 you want in your beer.
This chart will then tell you how much pressure you should set your regulator at.
This and
this will help you with calculating the line lengths based on that serving pressure. After lots of math, you'll find almost everything you want to serve will fall into the above short answer, although there's nothing wrong with having 4 different serving pressures and line length.
Hope this helps.
ETA: Also, like one of the links says, make sure the lines are as close to the same temp all the way from keg to faucet as much as you can. This alone will screw up serving more than anything else. If you built a keezer, put a computer fan blowing air from bottom to top to help keep it circulated. When I first built mine, I had 10 degree temp differences from the keg to the faucet, and just moving the air around fixed it.