I second the idea of using something to scrape off the tape. (I often use a credit card edge.) Sticky tape is my second go to method. FWIW, I usually remove the masking from the top of acrylic, especially when engraving. The masking can get gummed up in the engraving and can be hard to clean. It’s a lot easier to take off one big piece than deal with all the little cut pieces later as well. Any soot usually wipes off pretty easily. I do leave the back masking on to prevent flashback marks though.
As far as actually cleaning acrylic, I tend to stick with a plastic cleaner. Alcohol can craze acrylic and cause minute cracks. I ruined a few big projects that way :-/
Something else that might interest you is @takitus post about defocusing when engraving on acrylic. Good stuff 