coffee spill on iPad, what should I do?

Water and electronics generally do not make happy bedfellows. Your iPad is not designed to be water resistant. While it will survive being splashed with clean water if immediately dried, it will almost certainly suffer irreparable damage if it is allowed to get wet, or is submerged for any length of time.

Beverages, in particular those that contain animal fat (e.g., milk) or sugar, can cause significant damage if they come into contact with electronic components or electro-mechanical elements such as switches.

As you indicate that your iPad had suffered significant damage prior to exposure to coffee, contact with any liquid will have almost certainly caused irreparable damage. Given your description, you iPad is more than likely scrap.

You might consider visiting the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) where the technicians will be able to test and assess your iPad - and you can explore your available options:

Genius Bar Reservation and Apple Support Options - Apple

Sounds like time for a new device.

Buy a new iPad