1. With no 'lockable' doors, the dero's and warbies who are settlers make themselves at home in the player house, as well as trader/provisioner Brahmin magically appearing in ground floor level rooms.

2. Settlers and others make themselves welcome to player sourced power armour...I just had an attack on Sanctuary, and Trashcan Carla is now wandering around in one of my modded sets, as well as a couple of settlers wearing others...and, guess what? You can't get the one the trader is wearing off her...

How many more years would it have needed to actually get this right before release?

Seriously, the cost of 'better games' from Beth is 'more [censored] glitches'...

Take your power core with you and they don't take the PA.

Yes...

Unless they just happen to have a fusion core in their pocket, then they're good to go. My weapon merchant @ Starlight Drive-in is always jumping in the PA, since she usually has at least one core for sale.

So, now I store my personal PA at Red Rocket (where I'm the only resident), and leave a couple surplus suits that I don't mind her using at the drive-in. The upshot: whenever she grabs a suit, she'll leave the core in when she gets out (or I order her out). I get a free core every time she goes for a joyride!

Also place your personal bed last, so the other beds are taken (or manually assign settlers to beds). If you want a personal space they never go make your personal bed up a few stairs (and remember to place it last), along with any other stuff you want to place around...they'll never wander in there.

1. Assign settlers to specific beds and they won't use yours.

2. Remove the fusion cores.

I've never seen a settler put their own fusion core in a power armor suit, and I have plenty of vendors at my settlements that have fusion cores for sale. I'd have to see that to believe it.

I've noticed only certain NPCs will take the PA, or loot weapons from containers. Almost like there's a "panic threshold" stat for each one. I may just have a panicky merchant, she's the only settler I have that does it.

I have my provisioner assigned to my bed and have never noticed another settler in it. I haven't noticed guard post settlers sleeping either so maybe you can use them.

Correct, guards do not sleep.