Well done mate. I think everyone should service their own bikes, you get to know em a lot better then, and it's a good time to spot other problems before they escalate into expensive ones!
I grew up with Motocross bikes - engine rebuild every 8 hours of use if you wanted to keep it running sweet - think yourself lucky! (having said that I wasn't exactly a pro so the 8 hours was more like 20 for me).
wrt the mpg you are getting, seems about right. I have an '02 curvy with fairing and i get 150 to the light riding normally on A roads, dropping to about 130 if I nail it everywhere or with more town riding.
Every bike i have had always has a bit of brown gunk in the airbox - nothing to worry about so long as it's just a trace.