After you've been off the grain ride for a while, your appetite will shrink. Ideally, you will be eating lots of healthy vegetables and fruits, and enough protein, but not too much.
When you first eliminate grains and starches from your diet, you might find yourself eating more protein-rich foods. In the long term this isn't a very good idea, because too much protein over an extended time can lead to kidney problems.
You can calculate your daily protein requirements using an online calculator. For example, there is one on this site.
My advice in the first few weeks though, is not to worry about this too much. Your body will be craving carbs, and it's more important to get this part of your eating plan under control first. It's not the end of the world if you overdo it a little on protein rich foods in the beginning. Then, in the following weeks, you can focus on replacing those proteins with more vegetables, and, to a lesser extent, fruits, which tend to be higher in sugars.
Nuts are a good source of healthy fats too. I like to carry a little container of almonds around with me, so I have a quick snack on hand when I'm on the go, and people around me are reaching for cookies and muffins.