The bits are as/more important than the tool, depending on your needs.
If you want to invest more into it, I'd suggest the one where the motor is separate from the tool & connected by a cable.
It's lighter & easier to use than the motor-in-tool ones. It's more of a professional grade.
Beyond that, there is a huge selection of bits, both Dremel brand and other brands. Sounds like you'd be after the cutting type bits rather than the grinding ones.
Whatever you get, practice on some scrap plastic, to get an idea of what speed you need to use. Too fast and it'll go crazy.