This thread is over two years old - it's best to start your own topic for a question in the future rather than bringing up old threads.
There's no way to tell exactly how much a hedgehog should weigh - there's too great of a range. They can be anywhere from 250 grams to 1000 grams and be perfectly healthy, depending on the hedgehog. If you're unsure if he's at a healthy weight, the best way to get second opinions would be to start a new topic and post some pictures of him from the side and above so we can see his body shape.
Free-feeding is recommended for pretty much all hedgehogs on this forum, unless there's a severe weight issue. However, you also want to keep track of how much he eats, since going off food is an early sign of illness. Put out at least 2-3 tablespoons and see if he eats it all. If he does, add a little more the next night, and so on until there's a little bit of food left (for extra hungry nights, or a mid-day snack the next day). Then you won't be wasting a lot of food, but you'll know he's getting enough to eat.
Side note about your food: Which formula are you feeding? The Feline Vantage formula looks pretty good, but the other two formulas are too high in protein.