1. For making an allegation of not paying the rent he must prove the landlord - tenancy relationship by producing the copies of the rental agreement or any other evidence for your stay there in the premises as a tenant.
As far as the money he has to return it to you, he is giving some lame excuses with false accusations that you had taken his gold chain etc., you may first send a legal demand notice demanding the money you had lent to him in the past based on the transactions details and also his confirmation through whatsapp about the receipt of the said sum of loan amount.
Your government job will not be affected for any reason due to this legal notice or the legal steps that you may take to recover your amount.
2. First of all he cannot approach police without any evidence, even otherwise, the police will not register the FIR immediately on receipt of a complaint form him in this regard. They will first summon you, enquire into the incident and then only they may proceed with the legal action if they find that the complaint is made out on the basis of the documentary evidences he may submit.
3. Read the above.
If in case of a FIR registered against you, then yo may better apply for anticipatory bail and challenge his false case properly in the trial proceedings accordinlgy.
4. No, it will not affect.