$489!!
45 has the larger projectile. Size of the handgun will vary.
Yes
Either platform can be larger than the other. The 45 has the larger projectile. Caliber is defined as the diameter in fractions of an inch, so .40 caliber is smaller in diameter than .45 caliber. Caliber can also be defined in the metric system, measured in milimeters. The .40 caliber cartridge is equivalent to 10mm in diameter. As noted, the size of a handgun can vary widely within one caliber, so it is perfectly reasonable to have a smaller handgun crafted in a larger caliber.
it is a little less powerful but not by much
It all depends on you, your pocketbook, your skills.
No. Only shoot the caliber printed on the barrel.
By pulling the trigger... :P
No.
The short answer is no. You should not (and normally can't) fire any ammo in a gun other than what it is specifically designed to shoot. There are some exceptions, such as, you can fire 38 special in a gun designed for .357 magnum.
100-500 USD depending on EXACTLY what 40 caliber mode you have.
A 40mm handgun would fire a bullet the size of a golf ball. No such critter. There IS a .40 caliber handgun (about 10mm). There are dozens of larger caliber handguns than .40 caliber. They include the .41, .44. .45, .455. .460, .475, .500- and several others.