Adam Thwaites has a freebie muzzle Flash and a matrix style bullet trail in his freebies

http://www.most-digital-creations.com/freestuff.htm

Since this is a prop, add to the scene not postwork, if you have P7 or 8, animate the visiblity, in P6 or earlier parent it to the gun and scale to 0.0001 (invisible to all intents and purposes) when not firing. I usually have the flash visible at 100% in 1 frame, then 50% in a 2nd frame then invisible in the next.

A tip I've found useful for positioning the muzzle flash is to reposition the origin (in parameter properties tab click display origin then the dials will be visible) so that it is at the back (muzzle end) this also helps when scaling the blast as the prop won't move away from the gun as it does with a central origin. As for smoke, if it's in a fast moving vehicle I wouldn't waste time (creating and rendering)

For lights yes a small point light parented to the barrel, solid yellow colour is what I use, remember point lights only visible in raytracing.

I guess you could have a left-handed gun, but the only ones I've seen in real life have been specialist hand-made guns. Bespoke shotguns etc. Otherwise they are mass produced to suit the majority of the population.

Enough answers?
cheers, Dave

Edit to add bullet trails are a movie invention, the only time in reality that a bullet can be seen is if it's a tracer round, otherwise not until a hole appears in yer chest