Great questions. Yes, you will need to iron the shirts so the ink cures and doesn't come off in the wash. Or worse, it can just fall off. If you have parchment paper, put that between the iron and the shirt and run a hot iron back and forth for about a minute plus a few seconds. If you don't have parchment paper, just turn it inside out and iron the same as above. You just run the risk of the print sticking to the other side of the shirt, but the risk is pretty low. Good luck! Screen printing is fun!
No, once you have a design and burn it into a screen with the emulsion, it will transfer however it looks. It gets laid down on whatever your printing on and ink is simply leaked thru the open holes in the screen not covered with emulsion. Important thing is if you plan on multiple prints and shirts you have a good stable surface the screen press is attached to so you can duplicate each press.