Nail Polish remover is not gentle at all, its usually acetone based which is great for removing paint.I hear Goo Gone and nail polish remover are best for the job.
3M is usually a good choice for double sided tape.
I never used one but there are decal removers which are rubber wheels you can run in a cordless drill. But I would start with a heat gun to soften it up then just roll it off with your fingers.
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