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.
@Fishd Interesting - how would i go about installing the Linux os on the other ssd? Like normal, through bios and the like, i imagine?
Also, may be a silly question but can both os access each others drive? Like, if i have files in my Linux os install drive, can i access said files in Windows, and vice versa?
@marcorudy if you have windows already, then add your second drive and run the Linux installer... depending on distro the installer should ask you which drive to use and then, crucially, where to install the boot loader. Choose the same drive as your Linux install (i.e. not the windows one).
Then, you should be able to use your BIOS/EUFI boot menu (by pressing F2 / F7 etc ... it differs depending on manufacturer) to boot between the two.
They will moly be separate though. Linux will probably read the Windows disk ok but depending on your install might not write to it at all, or maybe not reliably.
Windows on the other hand will ignore your Linux drive unless you install some third party software, and even then it might be flakey.