The 410 is one of my favorites. I've never had any problem with it. The max range is pretty much dependant on how well your gun is patterning, but like Mudchicken said, 30 yards is about right for hunting.

As long as the gun throws a tight pattern, I can see no reason why the 410 wouldn't work just fine. I mean, squirrels and 410's go together like cheese and crackers.

I've always used the 3" #6 shot shells. Shooting squirrels in a tree shouldn't be a problem as long as you have a clear shot.