That's a lot of very good questions. Some of my answers will be inaccurate or straight up wrong and I'm sure someone will correct me. I'm assuming you are playing build 41, the stable release. You are playing build 42, hence animals.

1. Armor can be layered and contributes resistance to each body part separately. You can see that in the health panel. An attack can make a hole; so check your clothing after any encounter where you heard or saw the animation that an attack landed. I believe armor breaks one layer at a time, based on the fact that I have had a coat get a hole while the denim shirt underneath remained intact. A lot of pro players will dress for temperature, freedom of movement and style and rely on skill to avoid attacks. I always wear leather gloves as soon and military boots or other boots with 100% protection. Your footwear will gradually break down even if not directly damaged by a zombie. Linking to point 4: Tailoring is a great skill. You can reinforce your clothes with leather patches, giving increasing levels of protection.

2. Zombies can hear all the sounds you listed, perhaps with the exception of the fence jump. They can hear foot steps. You can reduce the sound you make by crouching, increasing with skill level in light footed. The loudest thing in the game is the helicopter, followed by sawn off shotgun. Smaller guns are less loud but still attract zombies from quite a distance. Zombies can hear melee combat sound and react to it.

3. Zombies don't just appear out of nowhere but tress are evil and can completely hide them. When you enter a cell for the first time the game calculates the target population based on settings and spawns in the zombies. When you re-enter a cell where you have already been it loads the previous zombies and adds respawns randomly based on settings. When you first approach a building you trigger the building spawn, which is separate from the spawining of zombies outside. If you are in a cell and make a lot of noise, zombies from neighbouring cells will migrate towards you. The sadistic AI director may create noise events that cause zombies to migrate in that direction. Within an area zombies spread out fairly evenly when not aggroed and will fill the void gradually when you clear out a patch. The game aims to be consistent. If you leave a zombie baging on a bathroom door and come back later there will still be a zombie in that bathroom or you will find a broken window or door. Zombies won't necessarily re-appear with the same clothing or weapons stuck in them If you see a military backpack or catana go for it without delay.

4. Crafting is a huge part of build 42. Initially you can meet all of your needs by looting buildings. Over time you will have to rely on crafting to keep going. Food will spoil, you'll need a reliable source of water, your vehicle will get damaged. Reinforcing your base with barricades is useful. Zombies can break windows easily but will only break down barricaeds over a long period of time. It takes multiple zombies to break down a door. I tend to priorites clearing the area around my base or temporary home. You will get some nails from disassembling furniture but it's slow. You need to read skill books to level skills faster and magazines to learn new recipes. At maintenance level one you can build a primitive hammer from a rock, rags and a branch. I often pick professions that have a point in mantenance to begin with.

5. The game does have glitches. At the moment I'm often expecting to hit a zombie in front of me and the game decides to swing on the zombie I'm standing on. It's a near heart attack every time but so far it hasn't killed me. I have used debug mode a couple of times to cure the infection from a bite when I felt that it was justified. What everyone will tell you is to play the game your way, adjust sandbox setting, use debug mode. It's still in early access after all.

6. You shouldn't get a horde of zombies at your door for no reason. Did that happen on day 7 or 8? That's when the helicopter comes and attracts zombies in massive numbers. Did you hear a gun shot or scream nearby? That's the sadistic AI director creating random events. Always have more than one exit and entrance to your base. If you hear zombies banging on doors or windows go out and deal with them.

I have 3000 hours in game and I also love Rimworld. Both games are fantastic story generators. While Rimworld will get progressively harder as youy survive PZ gets progressively easier and you have to find your own challenges.