You have a fun and challenging sticker removal job ahead of you.
Reflective vinyl on Ambulances is very different to standard car stickers and much harder to remove as uses a thicker material and stronger adhesive.
The whizzy wheel will do the job, though wear down a lot more due to the thickness and toughness of reflective decals. My gut feel is you will go through a few wheels on this job.
Heat guns are okay, though a bit hit and miss (they generally don’t work for old baked on and cracked stickers, but okay for newer stickers).
For removing the adhesive, the best and fastest way we have found is using a citrus degreaser (this is the stuff people use to get grease off stuff. I’m not sure about UK shops, but in the USA it looks like this citrus degreaser (Note: the whizzy wheel will take off a lot of the adhesive)
Good luck with the job and let me know if need further help