Where are you applying from? There's no insurance requirement for the Non Imm O based on marriage in the UK, however there's no multi entry, only single entry.
Yep. You'll need it or I doubt you'll be able to board your flight. Whilst the 30 days extention is rarely refused it's not a given and the airlines know this.
HK is the only Country I know(now) that you cant get a Non Imm O based on being over 50. UK/Europe/Australia and Countries neighbouring Thailand Issue them.