Hi, new to posting (longtime lurker, hope I'm not being annoying).
Are you making artwork for a new cassette recording or using cassettes as holders for other things? Just curious, we love tapes in my house - and nothing is cooler than a handmade mixtape cover.
I think acrylic paint would work, as long as it isn't watered down. The only touching issue I can think of would be thick paint cracking, so thinner layers might work better. Also, your question reminded me of an artist I don't personally know but happily stumbled across and bookmarked - fantastic paintings on paper bags, his statement says it's acrylic paint.
Hope that helps, Laci