Breeding hedgehogs isn't like breeding other animals. Hedgehogs are notorious for being difficult when it comes to breeding, and confidence based on experience with breeding other animals would worry me personally.
I would also suggest discussing with him how you would split the costs - costs of any possible vet visits/emergencies, the cost of the additional supplies. The babies are born where the mother is, and when they're weaned, they'll need their own cages (and all the supplies that go along with cages). I would want to know who's going to be responsible for that. And, when it comes down to it - what if she dies? Will you be reimbursed somehow?
Where are the babies going to go? Are you going to be able to find homes for as many as 6-7 babies? (Litters can be as much as 9-12, though without having a second female that can foster, 7 would probably the most you can expect to survive.) You should have potential homes lined up ahead of time.
Whether she's a good choice to be bred depends on more than just having a clean pedigree. Body type, for one thing. Little things about the personality.
And, yes, because you own the female, you have the most to lose. It's not common, but not rare either. Mothers can die. Complications can happen. You always think it'll happen to someone else, not to you, but that's not realistic. The first time we bred, the female had a breach baby stuck inside of her for well over 6 hours. We had no way of knowing; we thought it was just a litter of one. Thankfully, she was able to get the breach baby out on her own, and it ended up being a healthy litter of three. If she hadn't gotten it out on her own, she could have died, or would have needed surgery to have it removed. That kind of thing doesn't happen a lot - but that's not the same as not happening at all.