I was quoted medical insurance at about $300/mnth for a 10k (lowering to 5k after 3 yrs) deductable, no co-pay above that. There are other similar options around too.

So I figured I'd need a ring-fenced 'virtual portfolio' in my core stash that (1) throws off enough cash to pay the premium [$3600], plus (2) would pay for day to day care [assume $1500] & (3) allow for some repayment of capital if required for a few years when payments could be $5k+

Assuming a 7% growth rate, 5% dividend, $10k contingency, and 3% inflation, I recon that's a portfolio of ~$110k.

At FI this would just be a fraction of your total stash.