For first time plots especially, I would not plant in the spring (can't tell you plan from your post). I would spend this spring summer controlling weeds. If you want to plant them in the spring, buckwheat is tolerant of poor soil until the amendments you are applying according to your soil test have time to work. Buckwheat will outcompete many weeds and improve the soil. It is a short term crop (60 - 90 days) and deer use it. They generally don't abuse it. If you can't get buckwheat to grow well it tells you something.
As for seeding rates, I like to shoot for between 60 and 100 lbs per acre of winter rye and about 10 lbs/ac of clover. It works with a pretty wide window. I would not plant clover without the nurse crop of WR. Perennial clover spend a lot of time putting down a root system. This give lots of room for weeds to invade. If you did plant them separately, the rates would be about the same. WR and clover don't really compete.
When you plant them in the fall, clover does little more than germinate. The winter rye pops up quickly. Young tender WR is the attractant the first fall. Deer love it when it is young. When spring rolls around, the WR takes off. It gets a bit more mature and is less attractive to deer. It takes up space that weeds would otherwise use. It also has a chemical effect (allopathic) on weeds preventing many weed seeds from germinating. At this point, the clover is using most of its energy putting down the root system. In a few weeks it begins to put on more top growth. When the WR hits about a foot tall, it is important to mow it back to 6 to 8 inches. This releases the clover letting more light get to it. You may have to mow a couple times that first spring. The WR will die naturally and the clover will fill in.
This explains why the seeding rates are similar individually or mixed. The biggest competition between the WR and clover is for sun in the spring and you eliminate that by mowing.
Hope this helps,
Jack
