Very few "seminar" applications being reported, suggest you choose a more mainstream soft power activity. Use the group search tool with keyword Jakarta to see what others have reported from there.
You don't a residency certificate from immigration to apply for an extension at immigration, besides that it's only good for 30 days. You don't need an agent.
Non O based on what? Being over 50? You have the funds in a bank in your name? You don't need a TM30, you don't need a residence certificate. You probably don't even need a lease contract.
you can do an in-person report from 15 days before to 7 days after, you can do an online report from 15 days before to 7 days before, you can do a mail in report from 15 days before till whenever it gets there probably 7 days.