I think you're better off getting the Tourist Visa which is valid for 60 days (Saves you having to extend the VOA after 30 Days).
http://indonesianembassy.org.uk/en/consular/visa-info/tourist-visa/
Also, it used to be possible to convert the Tourist Visa into a Sosial Budaya visa without leaving the country, not officially though, it was just exploiting a loophole (the Tourist Visa had the same number as the Sosial Budaya visa). I don't know if it's still possible but if you're going to get the Tourist Visa anyway then it's worth a try. I actually used to do this every year but it's been more than 5 years since I last did it.
I have an almost irrational hatred of agents and middle men as they tend to create more problems than they solve, so if it was me, I'd just try to extend the visas yourself at the immigration office and if they refuse THEN go to an agent.
Sorry if I'm repeating advice from above, but I really doubt you'll be able to just live in Bali indefinitely, there's been talk of them cracking down on people who just keep extending their Sosial Budaya visas. Still, just try it and see, the worst that can happen is that they kick you out.
RE: Health Insurance
If you want insurance as an expat, then it's pretty expensive. It's a lot more comprehensive and reasonable if you use travel insurance, but you'll need to really read the fine print because a lot of them have a limit on how long you can use it and they may also refuse claims if you look more like an expat than a tourist.
If I was you, I'd set yourself up with a years worth of travel insurance so that you've got time to shop around once you get here.
https://www.healthcareinternational.com/
Have the cheapest expat insurance that I know of, but I have no idea if they have a good reputation for paying out claims.
https://www.lippoinsurance.com
Lippo Insurance have reasonably priced Health Insurance for living in Indonesia but I'm not sure if they have English speaking staff in their offices.