Personally, I think small and simple is a good call. Tucked away in a corner somewhere near Radtown I have a little 4 foundation home with 4 metal doors. All my stuff is behind the last door so it would take 8 C4 charges to get to it… absolutely not impossible, but I don’t have to open 500 doors (exaggeration) to get to my stuff and most raiders will get a door or two into it and go “screw this.”
As for metal walls, I’d recommend it. They’re expensive and yes, you’re right, it may attract bandits, but they’ll have a difficult time blowing a wall down, something that’s much easier with wooden walls.
Still, the most important thing to me is visibility (or lack-thereof).
Also, don’t light campfires/furnaces at night