There's multiple big fishes and hairy fuckers here, but the easiest solution is to just run like fuck to the building. That after you get NV, that shit comes handy later. Also, be sure to either cut the wired on traps, or walk on the rails if you don't need the extra filter.
About the boss, just stay out of its way, and plant claymores as close to it's ass as you can. It'll die fast. Granades/bullets works too. You can buy new shit once you get into the church anyway.