Just let the new bunny settle in for a good 2-4 weeks before you do any smell introductions. Your new bunny will be pretty stressed out from the move as it is. Addie, if I remember, has only been spayed for like a month? So her hormones are still fluctuating, so it really isn’t the best conditions for any sort of prebonding yet. Give the new bun 2-4 weeks to settle, and when he seems comfortable you can start prebonding and swapping items (assuming new bunny is fixed). If the new bunny isn’t fixed there’s really no point in prebonding yet as his scent will change after his operation.

How exciting!

I don’t think there is too much value in having the carriers side by side. The idea with the stress is that they will snuggle together for comfort. Some people like to bring the new bun home in the same carrier as the other, but I’ve always preferred to just let the new bun settle in a bit before launching into things. I think people usually opt to do the car ride home together when they are planning to just marathon them straight through, like if they are getting two new un-bonded buns, so the whole home is neutral.

If you do opt to do some car rides at some point (I’ve always found them helpful), I prefer to use a large plastic bin over a carrier. Then have a helper drive, and you sit in the back with the buns. The bin allows you to easily prevent any fighting or nipping. I think with my last pair I eventually switched to using a carrier once I knew they wouldn’t fight in the car.

Best of luck with your new bun! And that’s good news she’s a he. Most people say boy/girl are the easiest bond.