How do you decide where a species belongs in a food forest?

I've hit an interesting design snag in my food forest planning, and I'm curious how others think through these kinds of questions.

One thing I've been wrestling with is where a particular species actually "fits" within the overall design. It's easy enough to know what conditions the plant likes, but that's only part of the puzzle. I'm finding myself asking questions like:

Is this species primarily a productive crop, or is it more valuable as a support species?
Does it belong close to high-value fruit trees, or is it better on the margins?
Should I be thinking about its role over the next 5 years, or where it will fit in 20 years as the system matures?
How much should its ecological function outweigh its yield?

I keep coming back to the idea that in a food forest, every plant can fill multiple roles, but that almost makes the design decisions harder, not easier.

I'm interested in how other designers approach this. Do you start by defining the function you need in a particular space and then find a species to match? Or do you start with a species you really want to include and then build its guild and surrounding system around it?

I'd love to hear how others think through these kinds of design decisions, especially when a plant seems like it could fit in several different places.