Can I stay in Thailand for 5 months and obtain health insurance this year?

Border closed

Get yourself a Multiple Entry Tourist Visa (METV) before you come. It's good for 6 months and every time you enter you get stamped in for 60 days

If over 50 get a 90 day non o visa before coming to Thailand, when you arrive open a bank account with Kasikornbank ASAP, then get an agent to sort out your 12 month extension, no border runs required just 90 day reporting that the agents will do for about 100 bht.

Then renew every year with agent, the agent will sort out the 800,000bht required for the extension.

With a mtv you will still need to leave every 60 days land border with Cambodia is shut so you will need to fly out to return or face a long bus ride to Loas.

Doing multiple Border hopping has been stopped .

60 day exempt followed by a 30 day extension and then a border run. Dont see why you can't do this.

You can only stay in Thailand for max 90 days per year ( 60+30) or you have to apply for long term visa

No.

Other options are METV not sure how long that gives you .

Depending on your age if over 50 apply for retirement visa, the immigration are clamping down on border runs.