There are several Rev War Artillery reenactor groups in NY (probably F&I, War of 1812, and Civil War reenactors also); I would urge you to contact one of them. Hang out with them, maybe join them; they will almost definitely be willing to help you decide what you want, how historically accurate you want to be, how to operate one safely, and where to get "stuff".
I have two full sized replicas of British Light Infantry 3 Pounders. One was made by Cannon Ltd, Coolville OH, (now out of business), they made the barrel and carriage. The other tube came from Gilmore Ordnance in Ohio and the previous owner made the carriage. Making a carriage is not easy; think carefully about your skills, time, and dedication.
You do need to think about feeding them, my Cannon Ltd 3 Pounder has a sub caliber bore of 2.5 inches and uses 3 oz charges of cannon grade, 2FA, or 1Fg powder; the other is a full 3 inch bore and uses 4 oz charges of the same powder. They can get expensive.
They are a blast though, we shoot ours in the backyard for special events (New Year's, Christmas, birthdays, when people come over...). My two guns are part of our reenactor unit, the 3rd New Hampshire Regiment; we are in the process of gaining Artillery Company status with the Continental Line this year and expect to be at Old Sturbridge Village and Fort St John's, Quebec in August.
Here's a photo of the two guns in battery (the near gun is from Cannon Ltd.):
And one of the muzzle blast:
Yes, the girl is my niece and she's wearing ear and eye protection.