You've got a long road ahead :-) With no programming or electrical experience, you're going to have to do a lot of learning on the way.
1. There's no way USB current will be enough to power your lights, solenoids, etc. You will need power from your wall outlet.
2. When microswitches are triggered, they tell a microcontroller that something happened. These microswitches are passive -- they do not "have voltage" or current, they simply do or do not allow current to flow.
3. An Arduino board can certainly signal a relay to open and close in order to control a 50V (or other voltage) solenoid. A solenoid can also be turned on and off with a transistor (fewer moving parts). Some wiring examples of how a microcontroller board can turn high-current devices on and off can be found here
4. You are right that you will need some kind of power transformer to get 50V DC (or whatever voltage...solenoids come in all kinds) from 110VAC. I suggest buying a ready-made switching power converter, like this
5. Having a microswitch close then firing a solenoid will be easy once you figure out the electrical part. Focus on that first! Look at some of the example sketches available and get some basic electronics knowledge.