Mass Effect - sub missions

Once you get to a certain point you cant leave the mission, because the mission requires you to drive the MAKO down this long channel/corridoor type thing and a shield stops you turning back at one point, from then on you cant go back as far as i am aware.

However what the other guy said is true, you can start a new game with your char you used to complete the game, and you will retain your lvl, experience, items ect, i think it also unlocks Spectre Items on the 2nd playthrough and they are pretty powerfull, allthough i love the GETH assault rifle.

Some of the mods i have on my weapons stop them from overheating, so i pretty much have infinite fire on most of my weapons, i cant recall what my level is though, its about 48/49, but thats my 2nd playthrough standard male shepard.

Im playing as a Female Renagade Shepard to, so i can get some achievements related to that, and different endings.

Sorry, i have no idea, i dont ussually chase acheivements untill after i have done most of the game, i have missed loads of side missions, id like to know myself actually, not tried to get the kills with weapon types ones yet, but im trying to get the acheive for renagade / paragon on my other playthroughs and the lvl 50 and lvl 60 ones.

I think it would be best to assume that it only counts in one playthrough, i could be wrong, but there are so many enemies to kill it shouldn't be that hard to do.