You should really leave this to a gunsmith.
No
If you want it to be exclusively a scoped rifle, the best mount would probably be the one where you actually remove the rear sight aperture, and install a base for a scout scope mount there. If you're looking to install a reflex optic, and have it cowitness with your iron sights, then your best option would be the MAK rail.
No. Iron sights or peep sights (aka aperature sights) are the only type allowed for the merit badge.
Pretty much the same as any other military rifle sights, except for the ones with anti-aircraft sights. These folded OUT to the sides of the rear sights. The idea was to permit a rifle to fire ahead of an aircraft, which would allow the airplane to fly into where the bullet was headed.
Meters
Receiver, stock, barrel, sights
telescopic aperture battle
This refers to adjusting the sights on a rifle for elevation (up/down) and windage )left/right) so that the sights are pointed to the place that the bullet strikes at a given distance.
900 meters, depending on the rifle, sights, and skill of the user.
Bargain brand.
About 300 meters, depending on the rifle, sights, ammo, and skill of the shooter.
$100-$200, if you have an excellent condition rifle, complete with all sights.