My take, for whatever it's worth: Having multiple regulators allows you to serve different brew styles simultaneously at their appropriate carbonation levels, so it comes down to how many styles you want to serve at a time, plus one (or more?) lines for initial force carbing if you want to do that.
If I were to do it over again, I would have one primary regulator, set at 30 psi feeding a 4 outlet manifold; 2 or 3 of those would feed secondary regulators set to desired serving pressures, each with a 2 outlet manifold. That allows feeding 2 kegs at each of 2 or 3 serving pressures. The remaining 30 psi line(s) can be used for soda water and/or initial force carbing.
What I do have, because I did it a little at a time, is 3 primary regulators, each feeding a manifold. My keezer holds 4 kegs. I can connect any keg to any regulator (max of 2 on a given regulator). One long line allows initial forced carbing outside the keezer.
Because 3 regulators on the tank makes the 10 pound tank unstable, I hung the regulators on the collar and connected with a high pressure hose.
Note that secondary regulators are designed for low inlet pressures. You can not connect them directly to the CO2 tank, you need to feed them from a primary regulator.
Please share whatever you decide and let us know how it works out.