Wow - I am excited for you!
I travel to the US (Philly and Boston) regularly for work and never had any problems with diabetes supplies.
I have an insulin pump (your profile is blank so I don't know if you have one) . It is only the pump which makes the security guys aware I have diabetes. I always politely but firmly mention it cannot go in the body scanner. They are cool with this and do not pressurise me to do so (unlike in the UK). But there is usually a wait for them to find someone to do the manual pat down. And they will NOT touch the pump at all,
So, unless you have a pump, I wouldn't expect any questions about your diabetes.
As I travel for work, they pay for my travel insurance so I cannot comment on the cost. I would just highly recommend you get insurance that covers pre-existing conditions. It may seem expensive but it will be much much much more expensive if you are not insured.