Good morning!!
You made such a good decision to come on these boards. 3FC is so so helpful in staying on the WW plan.
As for flex v core, do whatever you feel like, and you can always switch if you don't like it. personally, i'm on flex, because i need to count and i don't trust myself to just stop when i'm full, but i keep toying with the idea of changing over eventually.
good luck with whatever you do and
s