Marco Rudy
Fishd@marcorudy I’d suggest:
1) Not dual booting, Windows finds ways to screw dual-boot systems
2) Separate SSDs and use the BIOS / EUFI to switch
External SSDs tend to be a lot slower and still end up with issues.
Bryan Redeagle 
@Fishd @marcorudy This is how I have it set up. Separate internal SSDs. It boots to Linux, which has an entry to boot Windows.
I installed Windows first, which allowed my Linux install to find Windows and add it to the boot screen.
@bryanredeagle @marcorudy Yeah, it's doable but folks often experience issues after certain Windows updates as it will wipe your bootloader and either fail to boot completely, or only allow you to boot Windows until you fix it using a Linux live CD. But it's very config dependent.