Extender Can I plug 2x keyboards and 1x mouse at remote location of a KVM extender

I'm looking to extend the dual-video console 1200 feet away from a computer.

The computer is 7 years old and uses VGA video.

I'm assuming I need to extend over fiber because of the distance. I can do either SingleMode or MultiMode fiber.

I couldn't find a dual-video VGA KVM extender over fiber and so I found one supporting DVI: FDX-M2U by SmartAVI.

Will this device work for me under the following conditions:

1) On the console end I have two keyboards and one mouse I need to connect. Will this work if I connected a USB hum, say, to the Keyboard port on the extender, then connect my two keyboards to the hub (while connecting the mouse directly to the extender's mouse port)?
P.S. Can I connect the hub to anyone of the two USB ports on the extender?
P.S.S. If this can work - does the USB hub need to have any special specifications (e.g. powered? any particular brand? supporting any particular USB speed?)

2) The 2nd keyboard I need to connect is actually a proprietary keyboard with a DB-9 connector. Can I use a serial (DB-9) to USB adapter which I will then plug in as the 2nd keyboard (as described above)? Will this work?

3) Since my computer has VGA video and this KVM extender supports DVI-D video, I guess I would need a video converter (convert the VGA output from my computer to digital DVI before making the connection to the extender's local box. Will this work (or cause any problems)? Is there any particular converter (in terms of feature set) that I need to consider?

4) Finally, might you be able to recommend such a dual-video KVM extender over fiber that natively support VGA video, thus sparing the need for video conversion?

Looking forward to your response - Thanks for your help!

P.S. I'm in the process of finding out what video resolution is required by the computer, but being that it's an old one I suspect it is not too high.