Lemongrass - tall
perennial bunching grass
needs: sun?, 3-4ft space?
yields: flavoring, repelling snakes?, preventing the encroachment of other grasses?, biomass?
Yerba Buena - I think this may refer to a number of different species, but if it is a mint, then:
needs: probably a moist spot, partial shade?
yields: tea, insectary, ground cover
Wormwood - I don't know this, and it depends on what specific plant
?
Lemon Verbena - shrub that can take some shade, leaves for flavoring
?
After looking at all the properties of these plants and the space you have to work with, you can start making connections between these elements.
What roles might the plants you have play?
Yerba Buena: ground cover, insectary, biomass
Lemongrass: provides shade
Wormwood & Lemon Verbena roles: shrub layer
What kind of roles are missing from this ensemble? Some I can think of are:
-Nitrogen-fixers - peas/beans might fit in a small system like this. there are a variety that grow in hot or cool times. From small annuals to
trees.
-Dynamic nutrient accumulators - yarrow, comfrey, and many plants perform this role, with different nutrients and elements (such as N, P, K, and all the minor ones)
-Tap-rooted plants - these can break up soil to allow better
water infiltration
-Matt-rooted plants & ground covers - stabilize soil and prevent erosion
-Vine layer - what plants or structures could support a vine of some sort?
-Tuber layer - what could be growing under the ground amongst these plants?
-Insectary - get a variety of these to attract different insects, different times of year, etc.
-Biomass - produces a lot of material over the year, good to contribute to mulch & composting
Much depends on your climate, your
land form, what you use, etc., but hopefully this will help out some to get started thinking of it.