In your experience, what is the best belt setup? (Ie. Number of mag holders, critical accessories, location/orientation on the belt, etc.)
You didn't say what discipline you are shooting but I will assume IPSC. In IPSC, you can have a course of fire with a maximum of 32 rounds. Worst case, if you have 4 x 6 shot positions, that is 4 mags that you will need minimum. Usually you want to have 1 extra magazine to barney with (load the 11th round into the chamber) and one mag in case something goes wrong like a jam. That puts you at 6 pouches.
It is ideal to have a pick up magnet as well as some stages will be table starts where you magazines will be on the table and you have to decide how to pick them up when the timer goes off. You can use a stand alone magnet or a combo pouch and magnet.
Personally, I like the DAA Deluxe magnetic pouches as they leave the majority of the magazine exposed which makes it very easy to reload. I would suggest setting up for bullets out as that gives you more space on your belt. With the exception of open division, all your gear has to go behind your hip bones and the bullets out profile allows you to move the magazines closed to the hip bones which is more ergonomic to grab rather than when they wrap around behind your back. You will need to initially spend a lot of time to set up your pouches to provide the easiest and most ergonomic locations. The DAA pouches can be canted do you can get the most ideal angle to grab them. You want to be able to grab all your magazines without feeling you are bending your wrists and hands at some oddball angle. Try to close your eyes and grab a magazine. If it feels odd, adjust the pouches until it feels natural.
For holster, a race holster is going to be slightly faster but you do have a learning curve to get comfortable with them. They are faster because you don't have to lift the gun as high before you can clear the holster and start moving forward. I used the Alpha X holster which has replaceable inserts to fit a variety of popular guns. It also easily detached from the belt if you have to travel.
For belts, I like both the DAA premium 2 part belts as well as the new Lynx belts. The Lynx belts are really nice and stiff and you definitely would want the wratchet buckle if you with that option. The Lynx belts definitely will feel tighter on the body and that removal of flex can make for more consistent draws and magazine retrievals.