I have recently purchased the Raspberry Pi Desktop kit which has an mSATA interface... However, as SSD's are quite expensive these days and it only operates with USB 2.0 speeds, it occured to me I'd be much better off just to use a USB. I could just use a USB in another one of the USB ports, but I don't want to waste a USB port. I had an idea, which might be stupid, but is there anyway I could connect a USB to an mSATA interface? I tried lookin for a USB female to mSATA male but had no success. Any information would be gratefully accepted
You are already using a USB port!
The desktop kit has a mSata Connection that connects to the USB port of the pi. It comes with a little dongle that connects the mini usb port of the mSata adapter to the full size usb port of the pi. You are asking to accomplish this Rpi(USB)--->mSATA--->(USB Drive) Which there is no need. You can boot directly from a USB drive
If you need more usb ports you can use a hub
I hope this link at rasperrypi.org will shed a little light on the Pi USB.
Basically keep in mind the Ethernet and usb are controlled by the same chip that juggles these bottlenecking speeds of these connected devices. You can make a desktop from an RPi, but might be limited, where similar SoC Pi like devices might be geared for higher bus speeds and network bandwidth, but might be more costly than a simple raspberry pi.