First, there are real farmers that frequent this board and they can give you waaaaaay better and more in depth information than I could ever pretend to. But I have been playing farmer on a small scale for wildife for a few years now. Not long enough that I have it figured out, but long enough that I've made a metric crap-ton of mistakes.
Get a quality soil test. Your extension service website probably has directions on how to do it, but generally you want to dig down 4-6" and get a small sample from various spots around your plot. Remove any foreign material, let it dry out, put it in a ziploc, deliver it to your extension office and tell them what you are planning on planting. Your results should give you a matrix of data including, but not limited to: pH, organic matter, N, P, K. It will also give you recommended soil amendments for whatever it is you want to plant. E.g., if you choose corn it'll probably say to apply a crapload of nitrogen. If it's beans, clover, etc. it'll be way low on N, but higher in P-K more likely. But at least you know what you need to do to amend the soil properly.
Think of your "needs." You should try to plant to provide support to your wildlife at critical need times of the year. For me in Kansas that is 1) fawning through weaning; & 2) winter. Winter may be less critical in central Texas, but keep in mind that when season winds down most of your neighbors will stop their free corn buffet. That creates a gap in the local food source that you can fill. A distant #3) for me is providing an attractant during hunting season. For many people that is #1 but I primarily want health and nutrition. If I have good habitat and food I have faith the deer will be around. I can find them on my own.
Next keep in mind what you are trying to accomplish. Too often deer plotters get fascinated with having a "pretty" plot that looks like a farm field. While herbicide resistant seeds and "clean" plots can be a good goal (particularly if you're trying to eradicate certain problem weeds/grasses), it's not always the best. A weedy mix that is full of food is often best for wildlife be it deer, turkey, quail, dove, or non-game animals. It provides food, vertical cover, variety... In short it's more of a buffet than a single course. If you plan/plant right there is almost always something in the mix that is delicious and helpful.
3 acres is a good sized plot. Probably big enough that you don't have to worry too much about it getting destroyed before it gets started. So you have a lot of option on what to plant. Again, keep in mind your goal. Summer food? Winter food? A mix that allows you to accomplish both? Consider planting your plot in strips. That allows for more "edges" and animals love to feed along edges. It'll increase your utilization. Think about forage soybeans over production beans. They won't set harvestable bean pods very well but will provide TONS of forage during the summer. I don't have the size of plot you do so I plant a mix of things all together. Sunflowers, sorghum, iron/clay peas, forage beans, etc. If I had a nice rectangular plot like you have I would plant in strips/blocks and rotate. If you google "LC Food Plot Mix" you will find months worth of internet reading on the best food plotter I ever knew. Sadly he passed away this year from ALS, but his strategies are strong, do a great job of building soil, and provide food all year long due to the mix of his plantings and the rotation of crops.
Okay, I cheated and looked up the link myself. Since his death the QDMA forum has created a sticky called "
A tribute to LC (Paul)" and has stockpiled a lot of his threads in one place.