Tamiya's paint is known to be very hard to remove: The solvents for efficient removal damage the lexan, and the solvents that don't have no effect on the paint either. It's a strong point of the Tamiya Paint because it adheres well and it doesn't really matter what solvents (or fuels) it comes in contact with. However, in your case it can indeed be a bit of a pain.
The example you mention - nail polish remover - doesn't work if it's a no-acetone or low-acetone formula. Pure acetone will dissolve the paint,
but it will also dissolve the lexan!
As long as the paint spillage/overspray is not on the outside or on the windows I would use some fine (>800) sandpaper: The scratches will fill up with paint and you won't see them anymore.
On the outside or the windows you could try a polishing compound like Commandant, but I can't assure a quick result or a 100% scratch-free shell.
Lastly, bleeding at the windows can be solved with a window outline/accent on the outside of the shell. I usually do it anyway, but if the bleeding is bad often it helps to just make the accent a bit wider
