According to the Alabama Cooperative Extension, now is about the right time to be planting beets. I have done beets the last two years. The first year, I was very happy with the results(except that we did not plant enough). This last year was a bit more disappointing in that a small beetle of some sort attacked my beets and chard and ate more of the leaves than I was ever able to. This in turn stunted the growth of the beet roots and caused most of them to be much less satisfying (both in texture and in size).

Spacing: I do mine about every 4 inches with the intent to pull every other one as baby beets and let the remainder mature a little longer.
Fertilization: I have been adding a lot of compost to my clay the past few years, and I don't usually do anything else for the beets (though with just two years of experience, others may have better suggestions).

Steve