What can I sue a landlord for who refused to repair mold, heating, gas leak, smoke detector, paint, etc?

I just moved from an apt. i rented for 8 yrs. Mold fr. a water leak was covered up twice, heating never worked on 1st of 3rd floors, reported a gas leak 3 mos. before moving- not repaired, smoke detector was unplugged next door to stop it from going off- not repaired for 1 yr,, refused to paint in 8 yrs, carpet over 13 years old and disgusting - refused to replace, severe termite damage- not repaired, you could get in the slider door even when locked- not repaired. After I moved the heater and stove were replaced, the mold was removed, and he sent me a bill for $7000 for repairs that were not my responsibility. He said my rent was lowered due to the condition of the carpet yet the new tenants are paying $50 less. If I were to take him to court on a counter-claim, what would I be entitled to based on these conditions? What monetary amount should I ask for and what amount should I settle for?