In the picture below there is a circuit representing a solenoid beeing driven by a switch and a voltage divider. The regulator is a lm7805. My question is..How or can I controll multiple solenoids with one regulator, just using multiple (switch, resistors, mosfet) branches for different solenoids?
[Edit: picture cropped to reduce white space around it. Moderator]
As you are using 12V to turn a 'standard' MOSFET on and off, you don't need the 5V regulator.
That particular MOSFET, IRF540N, wants to see 10V on the gate to turn fully on.
You can make R15 a much smaller value, like 100 ohm, and leaving R16 as 10K and where it is, the gate will see
(12V & 10,000)/(100 + 10,000) = 11.88V when the switch is closed.
The 100 ohm will let the MOSFET turn on nice & fast, the 10K will turn it off pretty quick when the switch is opened.