Yes, as long as your sight you put on it are made for that rail style.
Picatinny rails are used to mount accessories to the firearm. These can range from optical sights, to lasers, flashlights, grips, or in the case of devices like the "Mastery Key" even other guns.
Possible, but, very, very, very, expensive.
I believe you're asking about the picatinny rail system. This was designed to allow for the easy installation/removal/changing of accessory items, such as flashlight, scope, sights, lasers, etc.
Well, you can get the regular bead at the front, you can get the Ghost Ring sites, or, if you're looking in the aftermarket, you have a number of options, such as Picatinny rail mounted flip up/down sights, or even reflex optics like the AimPoint.
I'm assuming you already bought the Flatline barrel. That is bad news, since there are Flatline barrels with Picatinny rails mounted on them. Unfortunately, there aren't many ways to mount a bipod if you can't put a picatinny rail on it somewhere.
If it has a picatinny rail you should be able to, so yes, I believe you can.
It holds true to real firearms, as well. RIS is Rail Integration System, which is sometimes referred to as RAS (Rail Accessory System). It's the rail system for mounting accessories, such as tactical lights, optics, foregrips, etc.
If you're referring to the distinction between a MIL-STD-1913 Picatinny Rail and a Weaver Rail, your answer is to use a pair of calipers. Weaver Rails have a slot width of .18 inches, with no standards regarding the spacing of slot centres. Picatinny rails have a slot width of .206 inches, with slot centres spaced at .394 inches. General rule of thumb is that, if it's intended for commercial, hunting or other type of sporting uses, it will usually have a Weaver rail, while military styled and tactical designs will have a Picatinny system (to include rifles dressed up as sporting guns, such as the 'Remington' AR15 rifles currently sold at places such as Dick's Sporting Goods). However, Picatinny rail systems are available for commercial sporting firearms and vice versa. In the case of Airsoft weapons, although they try to emulate designs with Picatinny rails, the measurements are probably Weaver, or closer to it, as most airsoft accessories are designed to be Weaver compatible.
It's not a guaranteed thing - a lot of times, they will, but there are also a lot of times when they won't.
Yes. The A5 stealth comes stock with a top rail therefore a BT or Tippmann sight can be screwed on.
Picatinny Arsenal was created on 1880-09-06.
First off, it's "picatinny" rail. Secondly, no there are no aftermarket rails for that model that I am aware of. However, a competent gunsmith may be able to machine the frame to act as such.