Looking at your idea makes sense and I think it will work just fine, but as the previous post said, 1000 lb would be more than enough. You can find winches in the 1000 to 1500 lb range for $100 on sale all day long. Check tractor supply. If you still have doubt about the load, put a snatch block on the cable, run the cable hook back up to your beam and use a hook in the snatch block as the lifting point. You'll double the winch capacity and it'll only have to work half as hard.