Depends on where you are in relation to air pollution, light pollution, etc. Technically, you'd be able to see every star within a 13.7 billion light year radius. Only thing is most of the light is so faint, it's hard to see without specialized equipment.
Depends on light pollution levels, your own eyesight, and where you're viewing from.
Probably 3 to 5 thousand.
billions and billions?