What do I need to know about extending my STV visa in Thailand?

Hi all 👋 Sorry for the weird questions. I have never requested visa extensions so it's all new to me... I've flown into Thailand earlier this month on an STV from the UK. I'm starting to look into an extension as ideally I'd like to stay the full 270 days. My current STV expires on 8th April but I'd like to get things ready a bit earlier just in case 😅

I have a few questions:

1. What's the Bangkok office location for the STV extension? Chaeng Wattana? (IF I stayed in Bangkok until April, that is, then I guess I can apply to the closest immigration office wherever I am? I don't know where I will be as I have loose plans)

1. What documents do I need to bring apart from an extension application form (I guess I can find it at the office?), passport, TM6 (needed?)? Do I need to buy another 3 months of travel insurance? With the same provider as bought initially?

1. I guess I need a TM30? I'm currently staying in a condo and my landlady said she'll do the TM30 for me. I presume I'd need to get in touch with the hotel I stayed at before this condo (still here in Bangkok) and ask them for this form? And the same for the Test & Go hotel? Do you need a TM30 for each hotel you stay at?

1. Do I need a police check and a medical document? I wasn't asked for these when I applied for the STV in the UK by the way

1. I presume I'd have to book and pay for three months' of accommodation and an outbound flight. I'm planning to move around with no fixed programme. When I did the STV I didn't pay for hotels in advance...

Thank you for your help 😊