If you can, wait till 6 months for the spay. Neuters can be done as soon as the testicles are visible. There's some new research coming out about how the female hormones help young animals build bone structure, and how spaying too early can be detrimental because of that. I think the current standard for spaying for most vets is for the bunny to reach 2lb before it is done. However, with some dwarf breeds, it may be a lower weight cutoff. Ask the vet about what he's comfortable with, and take the bone growth info into consideration. If you can't stand her hormonal behavior, then get her spayed. You shouldn't have to worry about pregnancy once it's 6 weeks after the boy is neutered, and he can probably be neutered around 3-4 months.