1. Is there an option to simply upgrade, or must I purchase both again as separate things?
You will need to purchase both of these separately but there is an upgrade discount for both of them.
2. If I do this, will I lose the skins and settings that I already have?
Upgrading from windowsblinds 10 to 11 on a windows 10 device will not effect your settings. The only thing that may change is if you want to skin a windows 10 or 11 styled start menu. If you use the Windows 7 style everything will be exactly the same.
3. If I upgrade to Start 11 and WindowBlinds 11, will I lose my settings and skins when I upgrade to Windows 11?
I am not 100 percent. But I do believe as long as you do not do a clean install of windows 11 (i.e. upgrade and keep your settings) you should be able to keep your windowblinds settings.
4. Does WindowBlinds 11 work as well on Windows 11 as WindowBlinds 10 does on Windows 10?
No, certain skins will look better on Windows 11. Unfortunately some of Windows 11 parts are tricky. Parts like explorer tabs can make certain skins that were created for Windows 10 look a little off. Fortunately, Windowblinds 11 does come with the tools needed to skin Windows 11 properly, you just need to find the right skins for it. So your overall pool of skins may become less unless you use windows 10 parts on windows 11 (this method may not be an option in later versions of Windows 11)
Addtitionally,
You could 30 trial start 11 and windowblinds 11 and if you are not satisfied you could easily roll back to start 10 / windowblinds 10 and still keep your settings.
Addtionally, if you upgrade to Windows 11. You should have a 10 day trial period to roll back to Windows 10 and still be able to keep your settings. Just make sure not to go past the 10 day mark or you will have to do a clean install of Windows 10 should you want to roll back.