Hi
In regard to eating free food yes you can as much as you need to feel satisfied regardless of how much that might be. There are speed foods as well in with the free foods that can help your weight loss.
in regard to syns you need to eat between 5 and 15 a day, it will help with your weight loss.
In regard to mixing red and green there are ways for example extra easy where you can have anything that is free on red or green, you still have your syns (but if you have different syn values you take the lower one) but you only have one 'a' healthy extra and one 'b'. There is also mix to max, but I am not sure how that works.
There is another one called success express and I have even less clue about that one, but someone here will be able to help and probably explain things better than I have!
Hope that helps
Liz