I was just curious to find out if planted tanks do better with hard or soft water. I use a reverse osmosis de-ionizing water filtration system that brings all the water down to 0 ppm total dissolved solids before it ever goes into my tank. That being said, it removes all buffer from the water and leaves only pure water with a baseline pH of 7.0. Does it just depend on plants that I have to determine the ideal hardness?

I think you will find that plants do need some of the minerals removed and you may need to add some back. For my use, I find I can find plenty of plants to grow in hard alkaline water. In St. Clair, I would expect your water to be quite a bit like what I had in the West edge of St. Louis. I'm not a big fan of RO as it seems to be one extra layer or work and I fully admit that is something I try to avoid in my hobbies! When you remove the buffering, you may find the PH difficult to hold steady.

"Does it just depend on plants that I have to determine the ideal hardness?"

Generally: No. However, there are plants that much prefer soft(er) water, so it is something to keep in mind when trying to grow various species. Simply reconstitute the water to 1-3 KH and 3-5 GH and you should be good to go. If you want to breed shrimp...keep the KH very low 0-3.