Well I mean it would be okayif it were too tiny, honestly. You're not going to be 100% concerned with whats on the screen. 2x2 is normal to me, because I'm not super picky about actual size... 1x1 would work for a debugger. I think there should be three focuses:
1: Get as close to authentic emulation as possible.
2: Make a feature that overdrives the 8x calc you are using so people have more flexibility in case they want a SUPER 84+ or 83+. for example, an 83+ with TONs of memory and storage, or an 84+ at 500% speed. lol just a thought.
3: Somewhat pander the emulator towards developers, not just classroom users. Developers are probably the only people who want to use it anyways, as a student I'd ask "Why use an 84+ when I have an NSPIRE RIGHT HERE!"
Also, allow for overclocking or underclocking. Maybe do a check and ask "Do you want to run it at this speed?" or add a utility in the options bar to over/underclock the calc during emulation as you see fit.

I have ideas, lots of 'em lol
Mostly because I was going to write a similar project, for the Prizm.