I use a graphic drawing pad. I also use photo shop. To make my stencils etc.. when it come to tshirt stencil I do not know if illustrator matters because it needs be in transparent with the black parts for the stencil. However, If you are using a multi press then a nice rip software and going IN RGB mode is nice.. I use separation studio it is really nice but i have only one press. My idea of multi color is adding several color to the screen and squeegee away or block out with tape the one i want a different color and use some squeegee again i do this for a hobby and not for profit .. If it were the later then i will buy a 4 -6 press station.. Hope this helps