Yes you can connect two monitors simultaneously and extend the desktop to the second monitor.
Yes you can connect a 500GB mSATA disk and use it as your boot drive.* (I am writing this reply on a NUC using exactly that configuration right now.)
* Note that using a 500GB mSATA drive is an expensive way to go. If you get the "H" model NUC with room inside for a second drive, it might be less money to buy a smaller mSATA drive as your boot disk, then get a 1TB spinning drive as a separate data disk.
The mSATA can reach the same speed as SSDs depending on the manufacture specifications but the biggest different is the form factor.
Here is a very informative link:
NOTE: These links are being offered for your convenience and should not be viewed as an endorsement by Intel of the content, products, or services offered there.