Personally. I would just get a readymaderc system. Thats what I did. they are scalable, you wont plow them up by mixing voltages. When you are starting fpv there are enough things to problemsolve with signal and grounding. The learning curve is high enough. Start with a goob base, then build from that.
For my first monitor I used a laptop with a usb input. Its a cheap way to go and has recording built it, make a sun screen out of black foam board and call it a day.
Save your money and effort for goggles. It because a completely different experience what I got my Dominators.