creating an apple tree guild

I am on my way to creating an apple tree guild! Planning to clear a bit more space under my apple tree. When the weather cools off, most likely in September, I am going to toss some seed balls containing nasturtiums and ?? I also plan to plant comfrey and garlic. My question is how much space is needed for the comfrey? I have no experience with the plant. Any other advice is welcomed, as this is my first experience creating a guild.

I'm only familiar with the sterile 'Bocking' cultivars. Comfrey tends to expand pretty slowly, but a mature clump might be four or so feet across, most of that diameter being the leaves.
I chop and drop my comfrey several times a season, but it needs a chance to build up winter energy reserves and the bees love the flowers.
I make sure it has a chance to leaf-out and flower before winter.
I avoid planting things that need digging to harvest, as apples have lots of surface roots that are easily damaged.
Other plants I really recommend are yarrow, Egyptian walking onions, fennel, clover, coriander, lupins, flowering bulbs...
can you grow black currants? They fit well on the shady side of the tree here in NZ.