no you can get the medical insurance here. This is my live stream from last Sunday. If you go to the 'description' there is a health insurance link. I use this company and Hammer Time Insurance Brokers are excellent.
They are very well connected with immigration. I would go to their office. Everyone I know uses them as either the UK, US, Canada, Europe zone or Australian passport.
Yes, once your non OA visa is approved you can come here on a one way ticket without any issues. It's exactly how we as a family came here 3 years ago.
On that visa non-O? No, you do not need a return ticket. I've personally flown one from Heathrow with Eva and Thai Airways on a one way ticket with the same visa you have.
A lot of people I've come across have used them for Bank Accounts and Visas. Totally stress free. They don't even fill their forms in. This must be an easy option.