Guns would seem out of place
There is no wrong way to play minecraft, but there are so many things to discover, like villages, temples, ravines (the cave you fell into), the nether and even the end. All of that can only be found if you venture into new areas and explore.
if you can pour water on it before it explodes, it may minimize the damage. Anything covered with water can't be blown up, so at least the floor will be mostly safe.
Lure it away from anything important, and pour water in front of you. Then stand in the water and hold up a shield (as you still take explosion damage). Then let it walk into the water and blow up.
Not really, unless you cover the whole thing with a layer of blocks (although that still may not work). Just rebuild with non-flammable blocks like cobblestone and hope you don't get struck too much. Also don't throw any tridents with channeling on them.
I'm pretty sure they are the same npcs as vanilla minecraft, just with different textures. At least, they are on wii U.
Wouldn't hurt to check a review of the pack, though. I never bought one on PC, so I can't be sure.
My computer isn't letting me see the image, but do you have hoppers directly over the chests? Maybe you should put more chests around it with hoppers too, just in case the items are missing the chests.
Do you have a stream of water coming from the spawn room to the hopper? It needs that to move the items.
Also, you could try making the farm slightly bigger to stop skeletons spawning outside.
Hope this helps!