First, crop rotation isn't mandatory. It is primarily a commercial tool as many home gardeners simply don't have the space to do it and their gardens do just fine. Amending the soil well with quality compost 2x a year resolves many of the issues that crop rotation is directed towards.

But if you have the space to rotate crops, even moderately so, then so much the better. How often ou do it and what crops follow other crops is more of a nutrient/soil amendment issue than a rotation issue. So your plan, in any form, is fine if it works for you. But keep in mind that for a plan to work it needs to be flexible. Otherwise detailed, overly-detailed, fixed plans tend to quickly fail and fall by the wayside. :)

There are many green manure crops - alfalfa (not small garden oriented, legumes, vetch, clover, mustard greens, rye, etc. - each with its own advantages and disadvantages, and those who use them have their own personal favorites so seed cost and ease of care becomes the primary factor. For example, cheap end of season sales on turnip and radish seeds can be just as beneficial as fancy crown fetch or buckwheat seed.

Which ever one you use it usually gets tilled in in late winter or early spring 4-6 weeks before garden planting time. In my zone I have much later first frost date than you so for me that often works out to any good day in early January when the crop has been frost killed and the ground is dry enough to be worked.

Your garden is small enough that you don't really want to waste crop growing space by tying it up with mid-season cover crops. You can easily do 1 crop for the whole bed over winter.

Just some thought to consider.

Dave

Here is a link that might be useful: Green Manure Crops