Unlucky with the grey gameboy it was a real steal at that price and would have snapped it up myself for resale if i wasn't trying to save money! I'm really interested in what this GB you are waiting on is now, i always love a little anticipation and it will be nice to see another collector expand their collection.
If you need to decent site to look at what editions there are, www.consolecolors.com
is a good start however they are missing a few editions such as the gold GBP, so you can use the wikipedia page to see any others.
I just looked at the Sega Game Gear variants and never realized there was so many, how do you deal with them normally having buggered screens?
Also, the original gameboys shouldn't be too hard if you go for unboxed, but stupidly hard and expensive if you are going for a complete boxed collection. Many of the Play it Loud consoles came in plastic cases with paper inserts which are nearly always missing.
If/When i finish GBP collection i might venture further into GBA SP as some of the editions are just amazing and they looks nice out on display, but again the cost will be worse than GBP seeming there has so many different editions. (Around 50ish!!)