It's Multi-Entry, which means it can be used any number of times during its six month validity period. Each time you enter you are stamped in for 60 days, and each 60 days can be extra further 30 days. That's why it's possible to get nine months from the one visa
Yes you can do that but remember you will only be stamped in up to the expiry date of your insurance, so perhaps revise the insurance before you border bounce so you get the full year