I had a great time trying to figure out whether it was worth carrying 10 rifles on an expedition or just one. Same with steel swords. I think my standard outfit ended up being one rifle (plenty of bullets) and five swords - though I'm still not sure if it makes much of a difference.
I can't imagine how long it would take to complete the game without cheating. I would manipulating the localstorage database from time to time.
Approximately 6 hours, not counting the overnight break while I slept and let it just sit there accumulating resources.
I made a lot of non-optimal decisions the first time through, though, seeing as how I had no idea where it was going. That combined with the sleeping time means I have very little idea of the minimum time required to play it straight through.
If I'm not mistaken, carrying more of the same weapon doesn't give you any benefits, it only means you get to carry less of other items. I looked at the JS code while playing and found the amount of damage each weapon does. In battle, this amount of damage was dealt when carrying multiple of the same weapon or just a single one.
Carrying one of each weapon does make a huge difference though, because you get new attack buttons.
I can't imagine how long it would take to complete the game without cheating. I would manipulating the localstorage database from time to time.