The big thing to look for is inputs.
Make sure there are at least 2 HDMI, and 2 Component minimum.
I have a 42, my dad just bought a 50 and even though those sound big, dont not buy a bigger model just because it sounds to big - they are never big enough once you have one.
Also, plasmas are really only usefull if you can bolt em to the wall IMO. Find a good place, 4-5 feet high for the low point of the TV. Also remember that Plasmas as best viewed in the dark so it would be best to find a place that doesnt have alot of external light.
Another option is a project, most "old folks" are hesitant and while the HD quality isnt as good as a good plasma, the screen is a whole mother times larger
MYK