Wild strawberries can take more shade than regular strawberries (they're actually a woodland plant). Red clover can grow to 36"; densely planted, the strawberries may not do well. Crimson clover is a little shorter (up to 20").
The problem with a question like this is that very little research has been done. Most info has been done on row crops and clean tilling.
My opinion is that Steve should plant a small patch and report back on how it works (or doesn't). Until someone does it, you'll never know the truth -- theory is often disproved because there are other factors that aren't considered. Ma Nature tends to keep some things up her sleeves.
Soil test needed! One thing I haven't mentioned is that one of the four trees is a peach. I think it is a Frost Peach because it produced decently with no mulch or companions other than the apples, and it didn't get that peach leaf curl.
I read in Dave Jacke's Edible Forest Gardens, Vol. 2 that apple guilds need 38% nitrogen fixing plants.
Would hay mulch have a good chunk of phosphorous and potassium?
paul wheaton wrote:Strawberries can be beat by damn near anything. So I don't think you should worry too much about them overwhelming your other guild plants.
Here i planted wild forest strawberries under peach and thornless blackberry letting other meadow plants and also planted mint inbetween. Strawberries are outcompeting mint! Mint will not die off of course, but strawberries are just crazy.
I think, for multiple groundcovers your best way is to mimic diverse meadow from you region.