Hi, I am also new to growing pumpkins because I recently found some growing in my backyard! I had no idea what kind of vine or plant was growing on a dead tree stump, but we have several small, larger than a softball, pumpkins growing.
I'm online trying to find out how to take care of these and when to pick them, etc, but haven't found much info until I found this forum.

Can someone recommend a good source of information?

I wouldn't worry about the leaves dying since you have so many pumpkins. If they are solid orange then go ahead and pick them it will cause more pumpkins to form. Don't pull the vines up it is common for older leaves to die late in the season and the growing tips to still be healthy. Let the pumpkins fully ripen (turn orange) on the vines.

This forum has a ton of information just search for whatever topic you want about pumpkins. Sounds like they are doing fine just let them continue to grow and pick them when they turn from green to solid orange.

Some of mine are already orange, so I should go ahead and pick them? I thought that they would be like melons, when the stem drys up then they are ready to pick?? If I leave them, they will rot? How long will they last once I pick them and how is a good way to keep them for decorations? It is only the 1st of Sept. (almost) and I really wasn't expecting them so early. Any suggestions?