How big is your patch in square feet and what kind of pumpkins will you be growing? I would rotortill your patch now and bust up those clumps of weeds. I would make a shallow compost pit (about 10-12ft diameter) in the area you plan to plant your seedlings and I add as many leaves as I could. Stay away from oak leaves, as they take way too long to compost. I'd throw in any organic compost from the kitchen and add any manure you can get. Cover the pile with semi vented black plastic (lets water through keeps heat in). I'd water the pile once a week till the ground freezes.Then in late March if the ground is thawed, I'd hit it with tiller shoveling dirt into the pile mixing it all around. Then I'd till the soil 2 more times before you plant.
Hope this helps