Welcome Jeffharp. With 10 acres of alfalfa, you probably are going to want a siclebar or flail mower. Neither would be good for the lawn so you will likely need a mower deck as well. You should be able to use both mower types on an older 2000 series John Deere. If you want to harvest the alfalfa for feed, then you may need something larger like the older 4000 series which might get too big to mow lawns. The old 445, x4xx, and x5xx are not recommended for more then 5-7 acres.