Will you have any problems with legal issues if the makers of the original stunts see you using similar ideas and being quite blatant about taking the whole idea from them.
At least *not yet*. Personally, I don't have any moral problems with what I'm doing. I think that good ideas SHOULD be copied as much as possible, but we live in a strange world with strange laws, where sometimes the wrong people are being protected. So, maybe there is a risk. I really hope that nobody will ever use the moral holes in the law for getting money out of me or Ultimate Stunts.
Luckily, the laws in the Netherlands are not (yet) as weird as in the US, and dutch judges do not only look at the letter of the law, but also use some common sense.