Welcome Lanaia!
It makes me happy to read you are adopting your foster rabbit.
Lucky her!
To address your questions:
1. It may, Or the shed line will move. You might see her coat become more consistent after she has been on same diet and in same environment for several more months. If you’ve never had a rabbit before, be aware they do shed/moult a lot! With some rabbits the moult line is more obvious because of their fur colour. For instance, if they have bands of colour down the hair shaft.
2. By now, you probably have noticed her routine. Many rabbits will just sleep through the bulk of the day. So a quiet area upstairs is not a bad thing. For other times, do you have the room to set up a dog proofed pen downstairs for her in the main living area? I think it would be a good thing for her to become acclimatised to your dog. Eventually, you might be able to have them spending time together under supervision. : )
3. Bunnies do really well with a rabbit companion but it is sometimes a process to get them to the stage where they are bonded to live together amicably. Not always, some bonds are very swift. You could look for rabbits that are known not to be chewers, but it’s no guarantee that they won’t start the habit. Or that she might start it doing it. Actually, a rabbit that has had it’s incisors removed due to dental health would be a consideration… They look awfully cute and manage food quite well, pulling it into their mouth and chewing with molars as normal.
My experiences of having rabbit pairs is they are a little messier too. Some single rabbits can be impeccable with litter habits. I think it comes down to if you really want a second rabbit. Most issues that arise can be worked out. If they had to be contained more, build them a bigger space and keep it interesting. etc. One consideration – if you do adopt another and bond them, you may have to separate Mina when you feed them so the weightloss plan is not in jeopardy.
If keeping her single, I do think it would be good for her to come into areas where you spend a lot of time when you are home. It should keep her active also – hopefully!