I know it is just a trainer board, but what are the possibilities and limits on it. Could I make it into a pc by adding a monitor, and alphanumeric keyboard, or is it not possible or very very hard to do so

I think you can do both of those. Keyboards are a bit tricky, in that interfacing to USB needs some complexity and even PS/2 needs some work beyond a serial port. Making up your own 64-key matrix isn't impossible but does mean a lot of physical assembly.

For some background info see
http://www.decodesystems.com/heathkit-et3400.html
http://archive.org/details/HeathkitManu ... sorTrainer

The ETA-3400 is the best and easiest way to do this. The only problem is they are pretty rare. They do come up on eBay from time to time. I sold my 2nd last one there about a year ago for $400 which was apparently too cheap as it sold in 4 minutes. I have not seen one there since, but then again I rarely look for them.

My last one will probably be buried with me.

Beyond that, you could easily create your own equivalent to the ETA-3400 using more modern parts and providing a whole lot more memory. You could dispense with the cassette interface as using a PC for a terminal will provide a means to load and save programs as well as giving you a video display and a keyboard.

If you really wanted to build a keyboard for it an Appple II keyboard might not be too tough to interface.

As for video, your on your own. Not my strong suit.