Yes. Check out last picture. Basically the vertical pieces are variable in length and attach to vertical pieces with a special connector (check the pictures).

The maximum height is your arms.

No, unfortunately that's not possible. But you could have triangles made from wood at the DIY store so that the bar has a straight ceiling again. The poles can be clamped between the floor and ceiling super easily and ultra firmly. I'm really happy with the system.

Yes, there are a few. See at manufacturer: https://shop.wenko.de/wohnen/regale-ablagen/teleskop-garderobensystem-herkules-basic#search:sSearch=Herkules&query=Herkules&first=0

The Wenko Herkules coat rack is height adjustable from 165 cm - 300 cm. Unfortunately, the stand cannot be adjusted to a smaller height.

Yes.