1 & 2) You can file IT returns only from this assessment year in respect of income earned in India during the financial year ended on [deleted]. You'll not be able to file returns for earlier years, unless you get notice from IT Department. You may check for your compliance related issues, if any, after logging into the efiling portal of the IT Department.
3) Right now you don't have penalty issues. If there is no compliance related issue, the chances of receiving notices are remote.
4) As your husband is the owner of the properties, the rental income will be assessed in his hands only.
The interest income will also be taxed in the hands of the recipients only in your case.
5) You may file IT returns online but it's advisable to do so with professional help.
6) You can get your PAN updated but it's not mandatory to file IT return.
Few additional points :
1) You should have offered Indian income also in your UK tax returns and claim double taxation relief.
2) As you have received interest on your NRO a/c, most likely the bank would have deducted tax at source. If the amount is substantial, you may claim refund, if available, by filling an application before the appropriate authority.
3) If your rental income is more than Rs 20 lakhs, you need to get registered under GST and pay GST also.