Solid state external drive for MacBook Pro (Retina, 15-inch, Early 2013

I have a technical question about buying an external solid state drive for my MacBook Pro. 

My MacBook Pro has: 

* Two Thunderbolt 2 ports (up to 20 Gbps)

* Two USB 3 ports (up to 5 Gbps)

I also use VMWare Fusion so that I can run "virtual windows operating systems on my MacBook Pro.  My problem is that my MacBook Pro has a non-removable solid-state drive that is only 500gB capacity, and right now I am down to only 20gB of free space.

Would it be possible to somehow make the external drive bootable, or in some way be able to have the VMWare Fusion & Windows operating systems running from those external drive, and not have a "speed bottleneck" from the thunderbolt connections?  I mean, 20gbps sounds pretty fast to me, but I just don't know...and I especially don't know if I can make VMware Fusion work if it is located on an external drive. 

My other question:  Does anybody know of a solid state external drive that connects with Thunderbolt (and not just USB 3.0).  I've been looking on Lazada and AliExpress and so far have not found one.