1. Yes, they can but they are balancing on 6 bolts with all the weight above that. You can pose them standing with support like a chair, wall, desk, etc. Most of us who have standing dolls just lean them against the wall. Personally, I stand mine with the back of the head leaning against the wall to avoid flat spots on the body.
2. Yes, they can be left standing indefinitely but you’ll want to have a slight lean against a wall or dresser to stop them from tipping forward unexpectedly. Throw some socks onto the feet to help keep them somewhat protected but otherwise, they can be left like that. I go a step further and lay a folded towel under them to further protect the carpet and feet and I place another folded towel behind the doll to keep them from coming into contact with the wall.
3. Dolls that have foot bolts exposed can stand with support indefinitely with good joints. One manufacturer has a standing option with unexposed foot bolts so that is meant for very short periods of time as the skin gets compressed.
I always have about 6 dolls standing against walls. It’s been 2 years for some.
5. My TPE doll has the standing option and it can stand 24/7 without any issue. I did extend the protruding bolts slightly beyond the sole of the foot and keep her in shoes most of the time. I also have her touch or gently lean on something for greater balance and safety.
