Let’s clarify what BootCamp is - it is a special VM shell to allow a Mac to run two OSs concurrently! Giving you the ability to jump between the two with a simple keyboard command cutting and pasting data between Apps which are running under the different OSs.
Here you appear to want a hard wall between as the OSs will run on different drives what we call dual boot. So you need to restart and using the Startup Manager you choose which OS to use.
If you want BootCamp the two OSs need to be held within a single drive. But that doesn’t set a limit of the drives usage! So if I had three drives I could have the first one be the OS drive, the second a macOS formatted drive which holds my Apps and Data when running macOS. The third drive would be Windows10 formatted drive which holds my Apps and Data when running Windows10.
Now that’s a lot of drives! I can do the same just using two drives here i partition the second drive into two partitions so I have the last two drives as virtual drives (partitions). Now with this setup you don’t need as large boot drive unless you are working on large projects.
There are other configs possible here as well! Creating additional partitions within the boot drive so the Apps and the data are held in different drives (3 partitions on the boot drive) but this gets messy! Unless you have a large enough boot drive. You want to have some elbow room on the boot drive for the OSs space for caching and scratch space
As far as OS count you need one copy of each here, if you use BootCamp or Dual Boot!
What could get you into trouble is setting up BootCamp and then also do a second copy of Windows10 on a second drive thinking that was required which it’s not.