Here is my philosophy: You can never have too many implements, and you'll probably regret your choices no matter what advise you take. Sad, I know. There are a ton of things I wish I'd done differently. Monday Moring Quarterback, hind sight is 20/20. That sort of thing.
But to get to the root of your dilemma.
If I understand this correctly, you are looking to turn an area into dirt to create a food plot? You have a tractor with a tiller. You want to get a plow and a disc?
How much space are we talking here? Do you have obstacles on this property? Is it sloped?
Plowing is great for hitting that reset button. But on a slop can cause some nasty erosion if not done properly. Also, plowing is great for fields or plots without a bunch of things in the way, like trees, rocks, etc. Whereas, simply tilling the plot, you can easily move around these obstacles and is a bit more forgiving with slops.
Running a disc is great, but you will probably need to drag a harrow or cultipacker behind it to further smooth out the soil. A tiller will do this automatically.
However, a tiller is slow.
I posted a thread on a similar subject, here:
Plowing with LS
To update that threat, which I should probably do, the owner recently sold that property for huge profit. The new neighbors have yet to move in. I don't know what is going to happen.
But to summarize, It was a large open field, with some slopes, that would take too long to till with my 6ft tiller. I was looking to pull a plow though it, then disc it smooth before planting. I was only considering this because it is a large area. A food plot, depending on size, you may just get away with only tilling it. Save money on the purchase of a new plow and disc.