One X Upgrade. What now?

Set up your X and then change it so that its your home console and you should have no further problems

You can redeem in on either you Xbox or PC it won't make much of a difference as long as you use the same Microsoft account for both. I have Forza Horizon 4 running on both my Xbox and PC since it's a play anywhere title and has cross save which is great,
that way you can play where you left off when you go from your Xbox to PC or visa versa.

EDIT: Just realized I read your question wrong. Yeah, it doesn't matter where you redeem the code. Any code can be redeemed either through the console or the PC as long as you're signed into the same account.

As long as you're using the same account anything you've purchased or redeemed digitally can be redownloaded through your Games and Apps on the new console. Game saves are stored on the cloud and will resync once you start them on the new console.

Instead of having to redownload everything, if you're using an external hard drive, you can just swap that over. Or you can use a network transfer between the 2 consoles. https://beta.support.xbox.com/help/hardware-network/console/enable-network-game-transfer-xbox-one

Should be no problem at all. Most of us here upgrade consoles and change our home console.

I don't think it'll have an effect if you do it beforehand, but I would set up the X first to make sure there are no issues before doing so.