I have some general questions to help me understand PB

Is using a low glycemic index or low carb index helpful to decide which fruits and veggies to eat?
Is it helpful to look for gluten free products when choosing foods?
Can seeds be used instead of grains? (i.e. Quinoa, Buckwheat, Hemp seeds, ground)
Is there a list of approved packaged foods? (i.e. LARABAR-Jocalat www.larabar.com or Laughing Giraffe Organics Gluten free Granola www.thelaughinggiraffe.com, Justinís Natural Classic Almond butter squeeze pack www.justinsnutbutter.com

Thank you very much.