I don't think you will find many that would call post #1 "unethical". It is just a risky proposition. The guy you draft may still sign, and then you have spent the #1 overall pick on a role player and you gave him $8 million (or even $10 million is possible, I think). I don't think anyone knows the exact % chance he will sign, but I think that it is in the 10-15% range.
Regarding your 2nd post, the guy will ask for more than slot money up front (slot money would be $4 million for the #1 pick), but I'm not sure how much more... I would guess it will be around $6.5 mill total. If he comes back asking for even more money after your initial offer, you do not have to give it to him, though, and you will get the compensation pick next year (#2 overall) if you don't. Just make sure to offer him what he is asking up front and wait for his response.