Ouch, level 5 breakdown is quite dangerous lands indeed.
You can't even see half the zombies in that shot btw. That is not a horde. That is the rush of zombies that responded to gunshots since I had to kill 2 feral zombies and had no suppressors. And that is the beginning of level 5, as in I just had begun the level and just ventured out for the first time. I'm standing on a tower and there are zombies surrounding the base as well. And a few moments later, even more zombies filled that area with a horde or two. And you probably cannot tell (took with phone camera off screen) but there are an abundance of special zombies.
I'm not sure by what you mean rucksack discussion, but outposts can only deliver up to 3 resources per day. And you can have only as many outposts as your home supports. I think it works wonders to help you to stop losing supplies over time, which is why the whole time advancing while not playing isn't so punishing. But you'll still want to gather your own resources to accumulate excess to build things, get influence, etc. since waiting days to get a small portion of the resources would take forever.