When do y'all usually plant your spring plot? And anybody know what I should plant around the hamilton area?

A lot depends on the size of the plot.

Small plots (around 1/2 acre), about the best you can do is a fall planting of a mix of wheat, oats and Ladino clover. The clover will just barely get started in the fall/winter, but will explode in the spring and last until around May/June before going dormant - longer if you get a wet summer. If the wheat/oats start to get tall in the spring you need to cut it back to release the clover. Planting white clover in the spring is a hit or miss proposition - usually a miss. It needs to get established in the fall. Crimson clover usually does OK with a spring planting.

For large plots of an acre or more Iron/Clay peas are hard to beat.

It will be about an acre

A lot will depend on how many deer will use the plot and if livestock can get to it. Cowpeas or Soybeans are hard to beat for tonnage if you can get the rains. Clovers or other legumes planted in the fall with oats will or can grow from the fall into the heat of summer allowing you one planting and lessor costs per year. Call Turner Seed Co in Breckenridge to get their feedback.

For spring I use 4/15 as a rule of thumb for planting as to what I plant up on top of a hill in some poor sandy soil I have been using WTI's power plant. This year I took over another plot that is has good (6.9 PH) dark soil I plan on putting out some lablab and mix it with some other stuff. Both plots are at least 1/2 acre and each year I end up making them bigger. The nice thing about lablab and cowpeas is they grow almost anywhere like oats. The ranchman is right turner seed is good and will ship to your door, and bill you.
Let me say this with livestock you will need to fence it, I go electric and plant food plots is addictive. The first time you see deer out there eating something that you planted for them you WILL be hooked. I hunt between Johnson City and Fredericksburg (lots of cedar and rocks) and while we have not grown any BC's yet the deer have gotten much "gooder". Have fun.