Chuck
Some thoughts from my experiences raising Christmas Trees:
I thought about going with the three point type as well, but ultimately backed off because of the high cost ($5,000), and the bulky set up.
Look down the road when you begin harvesting or cutting trees. With your 4 acres, you will probably want to re-plant in the middle of the rows you have harvested. This means of course, that the stumps will now be in the middle of your tree rows, either wrecking havoc with your mowing equipment, or tripping over them if you are backpack spraying. Your size Kubota is not going to fit down the standard 60" tree row spacing,
For these reasons, I went with a Steiner tractor and stump grinder set up. It does a fabulous job on any size stump, is self propelled, and is small enough to get down the tree rows.
Ventrac makes similar units. Both units are very pricey new, but they have the same basic design for 30 years, and there are great deals on used units from private owners. Stay away from the commercial golf course and goverment units, as they tend to be abused. Search "Steiner" under "Home & Garden" on e-bay right now for a great deal on a like new stump grinder for $800. Good tractors go for as little as $1,500-$3,000.
I am in the process right now of clearing next years planting area, and grinding Christmas tree stumps in the middle of the tree rows from our choose n' cut sales this year. PM if you want for some pictures of the equipment in action.
Check out the following links for some nice equipment. Look at the tree farm mowers as well. Very sweet set ups!
Steiner Home Page
Ventrac Home Page
Thanks
Bill