There is a IC chip on the logic board that controlled the screen rotation. (Gyroscope / aceloromitor). But the obvious option is check the setting to see if it's set to "lock screen" also the side switch can also lock the screen so I won't rotate.
The iPhone 6S screen is also held in place with adhesive, along the edges. Check out a few disassembly tips on the ifixit repair videos. Do not try to pick or dig out the sim card from the sim slot, remove the screen and push it out gently from the inside.
Unfortuntly you will need to replace the digitizer again, a common mistake is when the cable gets pinched between the glass and the aluminume frame. This happens when the digitizer cable get stuck to the adhesive on the back of the glass while installing the digitizer. Make sure the cable folds twords the lcd during install.
The aluminum Frame would need to be replaced. There is no fix for a scratch on the aluminum frame. It would be and expensive repair for just a scratch. But yes it can be replaced, contact your local repair shop.
Sounds like one of the touch IC chip has failed, and yes it's related to the phone being dropped. There is a known problem with the touch IC chips having oxidized pads under the chip cousing the solder to fracture or a poor solder joint. The only fix is replacing they touch IC chip. You would need to send it out for repair if you don't have the necessary equipment or skill level to perform that repair.