Yes, 'insurance' is uncountable. As with any uncountable noun, you can use it without an article, as in 'I need to buy medical insurance', or with 'some': 'I need to buy some medical insurance'. If you need a singular or plural countable noun, you'd use the word 'policy', which is the contract you have with the insurance company e.g. 'Can you recommend a good medical insurance policy?'

Yep, it's uncountable. You'd say "I need to buy medical insurance to travel to your country".