Rabbits have a difficult time maintaining their body temperature. That means that it isn't a good idea to switch them from inside to outside (or vice-versa) when there are large temp differences. For example, if bunny is used to living outside when it is in the 30s and 40s in the winter, it would not be a good idea to bring them in every weekend into a warm (probably 68F) house. That would be hard on them.
I would however, suggest that you consider getting a rabbit that is already litter trained. I know some people think rabbit rescues are full of problem rabbits (or ill rabbits) but that is not at all the case. Many rabbits end up in shelters because people just didn't learn enough about rabbits before getting them. They were disappointed either that bunny wasn't cuddly, or bunny got hormonal (and they didn't want to pay for spaying), or they just got bored caring for an outdoor rabbit that was rarely visited and became a chore.
The rabbits at rescues are vet-checked and fixed. Fixed rabbits practically litter train themselves. So by getting a rabbit from a rescue, you get the advantage of skipping the hormonal stage, saving $100- $300 on surgery costs, seeing the actual personality/temperament of your rabbit (not possible with babies) and possibly getting an already litter trained rabbit.
If you do house indoors, the rabbit needs to stay confined in his cage initially anyway. This way he can get accustomed to "his space" and learn where the potty is. This is true even with already litter trained rabbits. Anytime a rabbit moves to a new location, he needs to establish/ learn his territory and area, so that is why he needs to stay in the cage initially. (I mention this because even if your rabbit potty trains while living outside, he would need to learn it again for while he is inside because it is a brand new area. So if you want him inside, he needs to be trained inside regardless.)
When he does start to come out of his cage, it will need to be in a limited area at first to be sure that the potty training remains consistent. Granting too much freedom too soon is a major cause for potty accidents.
Might I suggest that you browse around my
site? I put it together just for the purpose of letting people unfamiliar with indoor housing of rabbits to see what it can be like. There is also information on litter training.
And it sounds like you are unsure about whether to get one or two rabbits?? You can read on the site about the potential difficulty in getting two rabbits to get along. Of course, if you get your rabbits through a rescue, you can get already bonded pairs! I can't express how much simpler this would be than the alternatives. The idea of getting 2 babies would be the hardest way to go. Numerous times have we here on RO heard the same story over and over again: [2 babies snuggle, get hormonal, begin to fight, have to be fixed, !!$$!!, have to be kept separate until fixed and then until healed, have to re-introduce and attempt to bond -- might work, might not.]
Anyway, if you like the idea of having them indoors to play with and enjoy, then I'd encourage you to just house them indoors permanently. I so enjoy having the buns about the house all day long. We can see them and interact with them so conveniently - in all weather and anytime. As I type, the buns are nearby. While we watch TV, the buns run around the carpet in front of us. It's just so much more like a family member this way.