We have just been sanding our Ali stage tanks. They come out really nice using an angle grinder fitted with a soft wire grinding disk (don't use a metal cutting disk )
I know a few people who have had friendly automotive painters do their steels. Don't have any names or details unfortunately. I would be interested to know how hot you could have the oven to bake the paint before it started altering the crystalline structure???
Ali tanks... use paint stripper or sand paper. Dont bother repainting.
Steel. I'd avoid taking back to bare steel as generally they have a pretty good cold galve coat. I'd simply give it a light sand all over , coat of cold gav then a coat or two of colour, which is exactly what I did 2 days ago to a 3L faber. Hyundai Polar white was the colour of choice although I do like Mazda Clearwater blue. ( I have a few dozen different car colours at my disposal).
Any car painter should be able to do it for you but I cant see them doing it for less than $200.