As long as we can still order seed new genes can be introduced, in a small plot, at any time. My goal is to easily grow good food. I really don't care how old

As long as we can still order seed new genes can be introduced, in a small plot, at any time. My goal is to easily grow good food. I really don't care how old the line is or what it is named. That just doesn't matter when growing for food. If you are buying seed for a specific variety that is already a narrowed gene line. If the saved seeds are producing for you it doesn't really matter how narrow the gene pool is. You actually want to narrow the gene pool that is what adapting is. All you really need space for is allowing plants to reach full maturity. Some plants, like carrots or radishes, get huge if left to seed. One fruit from most plants will give you more seed than you likely planted. Each seed in a fruit is a unique individual that was fertilized by a different pollen. Even with self fertilization the seeds will not be genetically identical.