Old iPhone 6S, worth repairing?

Display issue on iPhone 6s

Context: I have an old iPhone 6S 64 GB rose gold model. A family member gave it at a shady repair shop to replace the battery and the shop kinda ruined it. He gave it back in this condition.

Issues: 1) the screen touch is not responsive, it doesn’t work, it often 3D touches when tapping normally.

2)There are short bars at the bottom of the screen where the touchscreen doesn’t work at all

3) the battery drops way to fast for a new battery

4) the screws at the bottom are missing

I wanted to take this as a project and repair it myself. Where do i start with repairing this? Do I buy parts on eBay, does anyone know any reliable seller who can ship to India?