Just an idea at this point, but the plan is to construct a "home computer" using a raspberry pi zero, inside an server room keyboard that I pulled out of the recycling bin at my last job!
Based on the parts I currently have, it will have ports for HDMI, 2 USB host, Ethernet, and possibly a small battery. I'd like to include composite video and audio output if I can get my head round it.
One of the ps/2 to usb converters I ordered has arrived! It works fine on a Pi 2 and on Windows, but it seems to not get enough power off the Zero. Connecting everything to a powered hub seemed to solve this, but if I'm wanting this to work on a battery pack, this could be a problem.
I do have another converter on order, one that's a bit newer, and not built into a hub. We'll see how it goes when that gets here. Also on order is another Ethernet dongle, and a few other parts that will be useful... like a micro sd extension! This means I can have the micro sd accessible without cracking the case open every time, and will let me position the pi in the best place in the case, probably based on where I want the hdmi port to be located.
Only one. I'm going to eventually do a project using the SPI slave port to read a keyboard, so that could be used as a second.
I assume you're using the second port for a mouse. They're a little harder to interface - you have to send some commands to start streaming mode. That has to be done with a bit of bit-banging since my interface doesn't support sending commands.
So you're method of using a real USB to PS/2 adapter is probably the best way.
Here's what I use for a PS/2 interface: https://hackaday.io/project/9922-ps2pi