Core is pretty easy - you could always be safe and weigh things like pasta / rice / potato to make sure you dont go over.. i do that as I know otherwise my portions will be out of control!
As for snacking, you can snack but only fruit and veg.. if you want anything like biscuits etc, you have to eat them alongside your meal times..
personally i have found as well that if my meal times change (which they do ALL the time cause I am unorganised!) I struggle a little with Core - you should never let yourself get starving hungry or uncomfortably full, and sometimes its really easy to slip and do just that!
however if you decide to try it for a week, we'll all help you as much as poss! One great thing about Core (for me anyway!) is that I can have MASSIVE bowls of Shreddies and milk and not have to care how much! I just had a bowl tonight and it looked like what I would normally have on Core, and it was 7.5pts LMAO!