Hi Paul,
Regarding 2) I believe in this case, you would need Latvian health insurance - however a quote would be quite cheap.
Had my assistant check with Latvian driving authority - can confirm that for the first year of being a Latvian resident, you are free to drive on your Intl Singapore Drivers license. After 1 year, you would need to switch to Latvian by doing only the driving test. In reality, if you are only coming to Latvia once per year to renew your residence permit and not living there full time - can just keep driving with your current intl license, with no issue.