Ny way to know which floor you are building before it is built

It's impossible. They will never ask to go to a residential level with any spaces remaining, and the question mark behavior means you can't even be sneaky and evict someone after you see which floor they're going to.

Those characters are only there to patronize shops and unlock scenes, and it wouldn't make any sense to have a Boba Fett living in your tower and then have another one show up so you could unlock a scene with him.

You can't reorganize them in any meaningful way, sadly, but it might make less difference than you think.

The levels of the bitizens on the floor are summed together, so it doesn't matter which slot is filled by who in this regard. The total level of all the bitizens gives you a percentage discount on the stock time for all items on the floor.

Thus, if your bitizen order is 9 in the first, 0 in the second, and 9 in the third, it is the same as having 9 in the first two and 0 in the third, or any other possible order of the bitizens.

For dream jobs, the first dream job worker on the floor will always double the stock of the first item, regardless of where they are actually "working" according to the status of the floor.

Thus, if your first bitizen is working their dream job, they'll double the first good. But if you only have one dream job worker on a floor and they're in the third slot, they'll still double the first good.