has it already been done,where and when.

Biologically, yes. Physically it could be a bit of a challenge.

There would be nothing to stop it breeding with a bigger dog, though there would probably be limits due to physical factors. However the main problem comes, I believe, when the dog is ready to have its puppies - many times they cannot get "out" because they are too large for the birth canal, and a caesarian may be necessary etc. In short, yes it can be done, but it may endanger the dog's life to try it. So please don't!

yes, usually it's a male chihuahua and bigger breed female dog (because they can handle the dog size, if it were the other way around the female could die because the puppies are too big). just look in your local animal shelter, there's tons of mixed breeds everywhere with heritage from all three toy, small, and large breeds.

Depends how big. It can be very dangerous for small dogs to have large puppies, be careful.

if the Chihuahua is a male then yes it can be done but if it is female it can't be done because the mother would die because she would have to give birth to bigger pups

Probably, but it would be one ugly dog but I would think it is cute anyway.

all dogs can breed with all dogs that are other breeds.