Steve, wow, I'd love a field overgrown with lupine!! It fixes nitrogen and brings in beneficial insects! It's a healthy field!! Goldenrod, too, insects love it.
Are you going to make beds, or
hugel mounds or pits, or do an entire field? I would mow out some beds, use what you mow to mulch the beds, add layers of manure and whatever else you have until the mulch is very deep. Plant in the mulch. Allow the rest to stay in bloom until it's done, then mow the paths, use that as mulch on the beds. The grass, unless it's crab grass or something that inhibits growth, like timothy, is good for mowing and
should be smotherable with very deep organic mulch.
The chestnut looks pretty good to me, unless it hasn't changed in 5 years or something. Clip away some of the stuff around it, and mulch out in a wider circle, deep enough to suppress growth of new weeds.