1. I believe you should have made your 07 return by the end of Oct gone. If you do this online you can still be on time as it allows an extra 3 weeks. 2. It's per calender year.
Use an accountant if you dont know what your at, it will save you money over the long run as they will know the system to get the best from it for you.
Its up to you. I am unable to give you definitive advice without knowing your circumstances, but in general the latter option is suitable in many cases. As the earlier poster says, you really need specific advice to see what best suits you