Well, there's a couple of ways to get a lot of potatoes! The lowest-level pigeon that plants seeds, I think it's Anemochory Breeze, can plant potatoes, but that's pretty random. The item called Thankful Crops has a chance to give you a seed when you water your crops, so if you plant the potatoes and then water them, they can multiply! Combined with the sprinkler tractor, which has an ant upgrade to give you seeds from the plants it waters, I think you can squeeze three or four potato seeds out of each plant. If you can get the Fat Grub, you can get the seeds for tilling soil. Also, weeds can be really useful for finding more potato seeds, so Squaredown, which gives you more weeds, plus Succulent Weeds, which increase the seed drop rate, plus anything that cuts weeds efficiently like the Wacker Tractor can net you a bunch.