Megasquirt is a pretty complex install for someone who is not very good at wiring or tuning. Its a lot to just jump right into. With that said buy the parts to run a SFMU setup is going to cost you a lot more in the long run because when you switch to MS you will be buying a different set of injectors and a 1:1 regulator. If I were you I would start off with MS since you already have it and try to find someone close to you that can help you tune it or show you how to run it.

Here is the difference between the FPR.

The FMU is stickly a rise rate regulator, when boost starts it restricts the fuel return rising the fuel pressure 12psi for ever 1psi of boost, the extra fuel pressure forces more fuel from the injectors. This works but with fuel pressures over 100psi its hard on the fuel pump and not adjustable at all. This is with a 12:1 FMU

The SFMU has a regulator built in so you can adjust base fuel pressure and also change the rise rate of the fuel pressure. It works like the FMU but much more adjustable.

The 1:1 FPR lets you set base fuel pressure and raises fuel pressure 1 psi for ever 1 psi of boost. You use MS to control the injectors for how much fuel you need to inject.