I would avoid mains powered dremels if you can. They tend to be a bit too fast for plastic and burn it. I spent a long time looking for the perfect rotary tool for plastic and went through loads of models, and for the most part, was disappointed with the results. My other hobby is Airfix style kits and I use my rotary tool far more than I should! I also use the same tool at work for making machine guards from acrylic where you have to match the guard to the machine contours.
You can get some decent lower-powered 12-18v models that you can stop with your fingers if you really wanted to. Much better for plastic as they will cut and grind without needing to be as careful. Far more controllable than 240v mains ones, and far better balanced than the battery ones that aren't much good for anything. The 12v ones are also very quiet.
If you have money to burn I highly recommend the Proxxon 28 515 kits. It retails for just over £70 so it's one of the more expensive kits, but the design of the collets and the attention to run out that proxxon put into those units mean they are very friendly to use and have no wobble or chatter provided the bits are decent quality.
They also do a router and pillar drill attachment for all the proxxon rotary tools that actually works properly.
https://www.proxxon.com/en/micromot/28515.php
https://www.axminster.co.uk/proxxon-micromot-60-e-starter-set-105598
If the proxxon is out of budget then the rotacraft 12-18v RC18 kit is also pretty decent the power supplies for them are a little weak (tend to crack if dropped), and the collets are not even close to the proxxon. Closer to how a dremel vibrates. They work well enough and don't burn plastic on the lowest speed settings.
https://www.ebay.co.uk/itm/ROTARY-TOOL-KIT-60-PIECE-VARIABLE-SPEED-12V-MINI-HOBBY-SANDER-DRILL-TOOL-CASE-/202733989257
The best of the 240v ones are the single-speed models, that are controlled externally with a sewing machine foot pedal. The ones with a speed controller on the tool are pretty much all too powerful.
For actually grinding plastic there are loads of bits that work well. Sanding drums, Diamond burrs, Carbide burrs, Sanding wheels and my favourite of all is silicone/abrasive polishing pads. Those pads are not cheap but I've yet to find anything that is as effective whilst still remaining gentle.
https://www.axminster.co.uk/proxxon-flexible-silicon-polishing-wheels-477212
The Proxxon accessory list is pretty huge, but some of the highlights are:
Universal holder:
https://www.axminster.co.uk/proxxon-uhz-universal-holder-475557
Drill press:
https://www.axminster.co.uk/proxxon-micromot-mb-200-drill-stand-502021
Router base:
https://www.axminster.co.uk/proxxon-router-base-ofv-505907
Keyless chuck:
https://www.axminster.co.uk/proxxon-micromot-keyless-chuck-100804