That's a good thought WM.
OK a few things you should do.
If you have _Any_ and I do mean any thoughts that you might be using either software or hardware which is not compatible with W10 or does not have a driver for W10, then a good starting place is the
Microsoft Compatibility Center.
If you don't know your product key for Windows or Office (2010 here), then download
Magical Jelly Bean and record it on paper. Why paper? Because when your PC is on it's back with it's legs in the air, it's kind of hard to open the document you put it in....
If you have a printer, scanner, or other device connected to your pc (I exclude monitors, keyboards or mice generally), including wireless keyboards and mice, check with the manufacturer if you can't find it on the Microsoft site. Sometimes the manufacturer may have the file and not submitted it to Microsoft to release with Windows Update.
Get the Driver _Before_ upgrading to W10 and put it on a USB key or other portable media.
Personally I would use a wired keyboard and mouse for an upgrade this important if I have a wireless set. I know it should work but for the £7 or so it will cost for both at Asda, is it worth having your PC sitting looking at you and not responding to the keyboard or mouse?
Know what software your are running on your computer. Then you can compare the lists and see what Windows10 removed.
Press Winkey+r
Enter cmd into the window and press enter
type powershell and press enter
type the following in the powershell window and press enter
Get-WmiObject -Class Win32_Product | Select-Object -Property Name > c:\users\public\documents\PCapps.txt
You will find a file called PCapps.txt in your public documents folder. To find it, open Windows Explorer (Winkey+e), open Libraries and then open documents and select public documents.
If you change the line to
Get-WmiObject -Class Win32_Product | Select-Object -Property Name > c:\users\public\documents\PCapps2.txt
when you run it a second time, you will have two lists to compare. Easiest to copy the text into two different Excel columns, side by side and see which does not match.
If you have more than one machine, don't upgrade more until you have completely assured yourself that the first is done, complete and without issues.
Finally, a full backup is _always_ a good idea. External USB storage is not that expensive if you don't have any, it's worth getting it to have that backup. Only the system state and boot drives need to be backed up. If you have a huge second drive, don't back it up. I tend to take the whole drive which my C drive is on because I use 64 bit windows and it creates two partitions for the drive. If you only take C you wind up with a broken system.
Windows Backup is enough, but that presumes that you can restore it if all goes badly wrong. I'll do a whole point on that later.
That's it for right now, I'll be back when I've done a bit more looking and gathered a few more hints.
And last night I had a "Windows 10" icon in Updates Available, "2.7 something Mb" from memory - but this morning it's gone and I have a "No Important Updates Available" advisory. (The PC is set to automatic updates and Windows 7 updates are proceeding on schedule and as normal.)