Yes it's possible, both of them are in fact sort of related. Besides, it's beneficial for P2 as well because P7 will help to strengthen the accounting standards rules and principles.
Yes you can. But not for the June '15 exams. I think the availability to do the P papers in any order starts for the December sitting?
Yes you can take ,but only if you have passed your P1 and P3.
If you have not yet completed P1 and P3 you will need to pay for them too if you are paying for P7. However, it is very possible and I feel that P2 and P7 are the best combination of papers as the information gained in one helps the other.