Check Windows 10 hardware compatibility before taking any other steps, you could have the conclusion right there.
My advice (I am using Windows 10) would depend on if the OS to be replaced is Windows 7 or not, from Windows 8.1, my advice will always be yes as there simply is no reason at all to stay behind afaik.
Windows 7... It all depends on the compatibility of the programs you need to have running, your need to stay private and your mileage.
It is not as easy to stay absolutely private on Windows 8.1 and 10 as it is on Windows 7, but using O&O ShutUp10 gets you down to acceptable levels.
The remaining FUD includes processes communicating extensively with Microsoft and the store. Windows Explorer communicates with Microsoft on the net, WWAHost.exe communicate lots with the store and so on.
Personally, I can't help but thinking that last bit is more for people with special requirements or interests, such as myself who needs to know what communicates from a security perspective to either allow or block...