Clean install on 2 PCs

I have 2 PCs. PC1 has W10 Home, PC2 has W10 Pro. Both came from retail Win7 licenses. I am changing the CPU and mobo in PC1. I also want to do clean installs on both PCs, to refresh them. But I want to put my W10 Pro license on PC1 and put W10 Home on PC2 .
1. What do I need to do to get ready for the license switch beforehand. MS assignment? Anything else?
2. Where can I get a current ISO for the clean install?
3. Do I provide my Windows 7 keys during install and W10 auto activates? Or do I use the troubleshooter? Will I need to contact MS Support?
4. Is there an order that I need to follow as to which PC gets the fresh install first?
Thanks.

DHHJ said:

1. What do I need to do to get ready for the license switch beforehand. MS assignment? Anything else?

Make sure your digital licenses for Windows is linked to a MS Account:
Microsoft Account - Link to Digital License on Windows 10 PC

Make sure you have the product keys for your Windows 7 recorded. You can probably retrieve them from upgrades if you have not done clean installs before using showkey plus:
ShowKeyPlus

DHHJ said:

2. Where can I get a current ISO for the clean install?

Download Windows 10

DHHJ said:

3. Do I provide my Windows 7 keys during install and W10 auto activates? Or do I use the troubleshooter? Will I need to contact MS Support?

Yes, in that order. I would first try activation with the Windows 7 product keys. If that doesn't work then use the activation troubleshooter. If that doesn't work then contact Microsoft.

DHHJ said:

4. Is there an order that I need to follow as to which PC gets the fresh install first?

No.