According to my knowledge-
If you lack heavily in credits (40-50 general and / or professional credits) you should go for full plan service. They will guide you through every step for as long as you need.. Plus it covers re evaluation fee.
If you lack less credits like 5-10 general credit you can choose plan incremental which is probably just half an hour conversation .

I had choosen full plan and it helped me a lot! Hope this helps..