Talk to your vet about this.
It doesn't matter that much, it just depends on personal preference, whether or not they get along with each other and with other pets in the family, and if they are neutered/spayed. If they aren't neutered or spayed, you should be sure to get the same gender puppy if you do not want them to breed.
The female should be spayed (fixed) at about 6 months. Some believe that she should have a litter before being spayed, but the only thing that does is add more unwanted dogs to the dog pound.
you get them spayed or nutered.
A female dog should be spayed between seasons so you should count two months from the last season.
Spayed female cats are called just that - spayed, or fixed, female cats.
The earlier the better, so they can be spayed when they are 6 months old.
Keep them away from other intact cats of the opposite sex. It is much easier and less worrisome to have them spayed or neutered, however. Female cats will go into heat every 8 days if they are not spayed, and it is not a pleasant experience. Also spayed female cats have a largely decreased risk of ovarian and mammary tumors, and neutered male cats have a largely decreased risk of prostate cancer. If cats are neutered/spayed before they reach sexual maturity it will also prevent bad behaviors such as spraying.
The best bet to avoid accidental pregnancy, pyometria, and several types of cancer is to have your female spayed BEFORE her first heat cycle. This usually occurs between 7-9 months of age.
Not usually - a female goat would only get spayed if she had an issue with her uterus.
Most veterinarians will tell you to wait until your dog's heat (season) has ended before spaying as it is unwise to spay her whilst her reproductive tract is active. You should wait until her heat has finished before getting her spayed.
if she isn't old, of corse. a lot of dogs get spayed. she should be fine.
Not at all. In my experience, getting females spayed makes them a bit calmer and lazier!