You should look at building your base in an existing building as it requires a lot less resources to base it up. I have my current base in a drive through bottle shop....5000 hit point roller doors at each end, concrete building. I never go for a big wide walkway as I feel that too many can come to the fighting door at once...I prefer a single runway so that they have to basically line up to get to me.

3:08:00 You can always use ladders from ground to catwalk for them to have additional climb spots....that is what I do on the catwalk and it works very well.

I don't think a shottie is an Oh shit weapon, as it loads way too slow and even fully equipped does not have enough shells.....you really need an auto rifle. I use my spear, but I have everything to do with spears 100% maxed out...so I can hit hard, fast and every kill tops up the stamina.