HARLEY-DAVIDSONMens Electron Leather Boots

Q: If I wear a 10.5 with some room left should I get a 10 in this boot?

No it have to be 10 wide so the boots will be comfortable for you

Q: Is it ok to use a water repellent agent on these boots

I have no idea. But leather is leather. So why wouldn't you be able to water proof them. They seem to have oil on them now as new. FYI: I really like these boots. They are quite comfy walking too. Easy to get on with the zipper, but I have to also untie them. No problem doing that.