I am new to quilting and feel like I over quilt my projects. How do you determine how much quilting is enough and not too much?

the rule is... there is no rule. whatever makes you happy.
Some people like less quilting, some like more. I prefer more. I have also heard that the more quilting you do the more durable the quilt becomes.

That is pretty much the story with all aspects of quilting....whatever makes you happy, do it!! :-)

The batting package should say how close the minimum quilting should be. Some battings are more stable than others. You've asked a good question. Show us some of your quilts. :)

I get the impression that in recent years, the trend is for more quilting, rather than less - at least the winners of big competitions seem to be highly quilted.

Does the type of batting used make a difference in how much you should quilt it? I mostly used cotton and try to quilt no more than 5 inches apart.

technically -- the quilting is to keep the layers together. So there is no "right" answer. I think the quilting should enhance the design. I had a teacher tell me that there should be curves and angles in every quilt -- she said a geometric design should have rope or circles in the quilting

Sometimes overall machine quilting can kill a beautiful design. A good machine quilter can bring out the design and colors and improve the top. Whatever feels good to you is "right"

It's probably a throwback to my childhood, but I like my quilts thick, soft and heavy. And warm. That was the main reason for making quilts many years ago, no insulation in houses, nasty weather in winter, few stoves in each house, so everyone had to have warm quilts. The quilting was simply to keep those layers from shifting about as the sleeper tossed and turned. So it's up to you, as the maker, to do just the way you like.

Now we use them mainly as decoration, or at least make them so that we can show them off and bow our heads modestly!!! And if they don't like my quilts, I'd like them to just say what I was taught.."How interesting!!" Nothing else. A closed mouth maketh no enemies.

I really think whatever satisfies you is enough. :)

Your personal taste and what seems appropriate to you for that particular quilt.