Extend existing policy and adding countries

I have a policy started on 2/10/15 to 9/10/15 to UK. I intend to find a job and stay longer so I would like to extend my policy my questions are:
1/How long is the maximum period i can extend for my existing policy?
2/ I want to travel to Europe some times from UK in a short period such as over the weekend, what can i do if i cannot add more countries into my extended policy.
3/ if i buying the new policy with more countries added in when my existing policy expire, do i have the same cover and is there any exclusion/ restriction because i getting the polcy while i am aready oversea