Yes, 8 tooth gives you faster chain speed over a 7 tooth, but less torque to maintain it under load. Depends what you are doing with it, but stick with the 7 tooth and put a good sharp chain on it. That saw cuts good, just a little heavy compared to other saws of the era.
There are plenty of opinions here, mostly worth listening to. I have run that saw quite a bit and i wouldn't change the sprocket being a 60cc saw, but i haven't put one on there for the heck of it to see what it does. If the same chain will fit with the 8 tooth, it might be worth the experiment. Then you know first hand how much things change.
One extra tooth doesnt sound like much, but thats one extra tooth per revolution. Take that times say 10,000 rpm, thats adds up. Other folks here are more into sprocket swaps. Not sure if they have a cc range they would recommend. Usually on bigger saws i think. In the end, if you like it, run it!
That could be possible but I doubt it the person I got it from didn't do anything to it because he didn't like how heavy it was and used it as a loaner saw I don't think the air filter or even the fule filter was changed. The bar I don't beleive is original though because it is an Oregon.