My G3 is 5 years old and its never broken down, the hopup has broken ONCE and miraculously fixed itself in 10 minutes, and its only ever had one jam from a black elite BB.
some guns are extremely reliable, poorly upgraded guns and alot of stock ones are not. Again, the more you pay the better the gun, just like paintball.
as for protection, i wear a pair of ballistic goggles, thats it.
some gas guns have adjustable velocity, standard AEG's require you to change the spring.
there are decent cheap guns, but it will cost alot more to upgrade from a decent gun than from a good gun.
It's illegal to import anything that looks like a gun (except clear with orange tip) into canada.
and the milsim aspect depends on your province. Manitoba is very milsim (IE military style training, no hicap magazines and some ops have realcap limitations)