Yes, if you have 5V available use that, however bear in mind that the switching regulator (DC-DC converter module IIRC) is complete overkill if all it is supplying is your LED switching circuit. For low average current jobs as here, the 7805 is preferred as it is simple and cheap. It works by simply converting the unwanted volts to heat. So, say your power supply is 25V and you need 5V for your gate driver chip (or p-type small signal MOSFET). When your circuit draws 1mA at 5V, the regulator adjusts itself to act as a 20K ohm resistor so that it develops 20V across it when the current is 1mA, leaving 5V for your circuit. Thus the 7805 consumes 20mW and your circuit 5mW in this example (always in a 4:1 ratio as long as your supply remains 25V giving a 4:1 ratio with your desired 5V). The switching regulator would consume more than 5mW due to switching losses, leakage and parasitics, but would pay off at higher currents such as 100mA.
Also, about MOSFET selection, if you have 5V available use logic level power MOSFETs, if you have 10V or 12V use ordinary power MOSFETs. Avoid having multiple supplies whereever possible! If you have a choice, go with what's cheapest. A 7812 is about the same price as a 7805, maybe slightly more. Logic level MOSFETs were traditionally more expensive but I think that may have changed now. Logic level MOSFETs are popular and getting better all the time (used in phones, PCs etc).
cheers, Nick