I have a small/medium sized dog, a south Auckland special, with a bit of Jack Russel and Chihuahua in him and who knows what else and he occasionally has leg issues. He hurt himself jumping from a decent height one day and since then he's had a couple more episodes with it. Hasn't happened in a while thankfully, but he's due for a checkup soon and i'll probably get him x-rays and make sure it's nothing that will affect him in the future, if it is we shall deal with it, but i've been told it was probably just weak from hurting it the first time. Now someone has mentioned genetics it concerns me even more. Better to be safe than sorry.
I think issues could arise in any dog, I briefly looked at pugs a few years ago, but they apparently have breathing problems due to their short snout. I don't think anyone could give you a proper answer, some people say purebred dogs, others say mongrels have less problems. I don't believe that being a cross it has a higher chance of being a healthier dog. I guess at least if you changed your mind and went with a purebred dog you could talk to the breeder about any problems they might have. With my dog I have no idea of his breeding history and i'm just happy that the vet has said he's in good health! I think regardless it's a bit of a gamble no matter which breed you choose and you just have to be prepared in case anything terrible does happen.
In regard to desexing I paid $140 for my boy to be done which included pain relief but it may be cheaper in Auckland, I wouldn't know. I do know that it's more expensive for a female to be fixed, I think about $200, but that was in Taupo.