The keyboard/mouse breakout might have been for a different machine - the AXP 3000 uses straight KB/M and I think later versions of the VAXstation/DECstation have 3W3 video connectors and the keyboard/mouse combined port (some also offer separate keyboard/mouse ports for some reason, probably you use the separate if you have the box on your desk and the combined if the box is stashed elsewhere).
The 2000s have a 1-bit monochrome framebuffer - think Mac Plus - type video. For general utility you''d probably be better off with the VAXstation 3100, especially as I hear that it has the color framebuffer installed. There's a guide on how to connect a monitor at http://home.iae.nl/users/pb0aia/vax/vs3khw.html
, or you can just wait for a cable to show up. The VS3100 has separate KB/M connectors, so keep a mouse and keyboard for that. Your VS3100 will run OpenVMS, Ultrix or NetBSD (probably also some more variants of BSD).
The Personal DECstation is a MIPS-based (little-endian) workstation by DEC. It runs Ultrix by design and xBSD as well. Probably the fastest of the set here, but not a VAX.
The MicroVAX 3100 is probably a model 10, possibly a 10e. I'm not sure when DEC started putting model designations on MicroVAX-3100s.
For what it looks like you're interested in I'd consider keeping the VS3100 if I were you. Keyboard and mouse can be directly connected to the back, a video cable can be borrowed or cobbled together, and it will give you color graphics similar to the VAXstation-II in the picture. Keep at least the nicest of the VAX(something)2000s, they're interesting machines and are smallish, but the small disk, 1-bit framebuffer, and slow processors likely make them undesirable daily drivers (the VS3100 will be at least 3 times as fast as the 2ks) Keep the other one for parts or swap material if you want - they can lay down the DEC format on ST-506-type drives, which can't be done on other machines without the DEC field service hardware (this makes them somewhat desirable in the old DEC community).
I'll check my cable boxes. I know I have a VAXstation external SCSI cable, and I'm not sure if the video cable I have is VAXstation or NCD X-terminal.
How many can you take?