Ok to put together all of these various posts,
A taller bush, I like currants, yeah those...north of the tree they dont like full sunlight
A nitrogen fixer,
A deep rooted plant to pull up nutrients from deep in the ground.....for me this year I will try alfafa for both the deep roots and the nitrogen fixing properties, this is the one everyone is using comfrey for or those radishes, jeruselum artichokes as well (google deep rooted plants)
A plant which will out compete grass...often bulbs but I am going with garlic chives
Plants which keep bugs away or which attract beneficial insects or even ones which the bugs will choose to eat instead....dill and the garlic chives are like that for me...near by is also fennel and beebalm as well as some purple thing i do not recall the name of.
with these one can add lower layer such as creeping thyme (which i might use this year but I am really not in a hurry to make sure everything is in place all at once)
below all this...mushrooms are possible as well or so i hear. I linked above some non-edible ones which could be used for soil improvement...I have my eye on those as well
With each recommendation above, fit it into one of those categories.
I am not too fixated on other peoples rules....I am using potatoes just outside the area where I expect any roots to be this year...when digging them up i figure it will mix up the soil. They are heavy feeders so wont leave nice nutrients but i will
compost the tops in place and hope it gives back. You see, my ideas on these things is that you try something and tell yourself it is ok to fail or not have a raving success your first time out. Keep the general ideas in mind and play with everything....remember sepp says yu should grow all kinds of poisonous plants too so everything need not be edible to you.