Thank you for your additional information.
Here is what I see as owed:
$450 rent for December (if unpaid), PLUS
$118.32 for 8 days in January ($450 monthly rent times 12 equals $5400 annual rent, divided by 365 days equals $14.79 per day, times 8 days equals $118.32) [See note below], PLUS
Damages (unknown amount). You say only a door for $100.00, landlord is claiming $350.00 (you don't say if he agrees as to only the door, or if he is claiming other damages also), PLUS
Any applicable legal fees, court costs, etc. (your post says that the landlord "is suing", so I assume that there are SOME fees (filing and process service, etc.).
NOTE: Since the landlord terminated your lease (if any) by asking you to leave (either through the courts or personally), he cannot collect for the days that you were no longer a tenant. Also, daily rent is based on your being COMPLETELY out of the apartment, unit is cleaned, ALL KEYS RETURNED and notice of vacancy to the landlord. If you kept any part of the apartment INCLUDING KEYS or failed to notify, then your rent would apply until you totally vacated the unit, or his demand vacancy of January 20th.
So, with all that in mind, I would send the landlord a letter CERTIFIED RRR. Detail your position and the amounts you think are reasonable.
Finally, the legal aspects:
You need to look at Kentucky Code KRS 383.580, it details what is required for your security deposit. For example:
1) The landlord is required to place your security deposit in a 'special' account used only for that purpose. And you are MUST be told where and the account number.
2) The landlord is required to provide you with a list of known damages BEFORE you move in and you are supposed to sign it.
3) Upon termination or end of lease, both the landlord AND tenant are to sign the post-tenancy inspection report.
4) Most important, if ANY of the above are not done by the landlord, the landlord CANNOT retain ANY of the deposit.
The appropriate law can be viewed at:
http://162.114.4.13/KRS/383-00/CHAPTER.HTM