Paper is more forgiving than T-shirts when it comes to mesh count. But if you are going to do photographic stenciling you may want to watch this tutorial:
It's surprisingly easy compared to making stencils by hand.....kinda.
You can reuse screens and if you want to make money you must reuse screens. You need emulsion remover for the type of emulsion you are using and a power washer to clean the emulsion out of the screen.
The emulsion is photosensitive. You add a activator to the emulsion then coat the screen, after the emulsion drys you place the film (transparency) on the screen, to get a good image you need to burn the screen under vacuum. The image can then be washed out. The reason the emulsion is easily washed out is that it is uncured and is not harden into the mesh. The black keeps the light form hardening the emulsion. I am assuming you are using a water based emulsion so you want to keep it dry until it is burned.