If you are being experimental, why not do a grid design common in agricultural trials?
Fukuoka mentions serveral times about weakening existing vegetation when introducing new species through seed balls or sowing -- be it manual hoeing, chickens, pigs, flooding, burning, etc...
Consider doing minimal disturbance treaments in strips (with replicates if you like). Then sow your seed mix in strips in the opposite direction (See figure).
I have found that if you seed too dense, a few dominant species best suited to the disturbance and site tend to dominate. (in my case I had
chicken scratched ground, did a spring sowing, and the mustard family dominated).
For sage, thyme, rosemary, your mint family sub-shrubs, I would be tempted to stick cuttings rather than seedlings. I think of these as stress tolerators, and they may not be as competitive in a humid herbaceous community, our 3 month drought greatly helps the competitiveness of these species. Mint is very aggressive and may dominate over time on a moist site - consider a sparse patchy planting, root cuttings under light
mulch is effective for mint and strawberry stolons. Root cuttings from horseradish also. Elephant garlic (actually a perennial leek) naturalizes well.
So given different regeneration strategies I'd imagine patches of modest tillage followed by seeding with patches of mulch, cobined with stem root cuttings and tubers would be optimal for this species mix. I'd be tempted to treat the whole patch with some kind of livestock prior to seeding to create regeneration niches, or at least do some cutting the previous year, leaving mulch piles to create dead spots.
Since you're an academic

... Consider Grimes theory of plant strategies, and the concept of maximum diversity through intermediate disturbance. I suspect there is a correspondance between disturbance and species for optimal recruitment.
Finally -- I don't understand the intent of creating three different seed mixes given the haphazard planting approach. Why not just one mix, and see what happens.
Finally finally... the species of grass may affect how the system develops over time. Grass is very competitive and not edible. I'd recommend actually understanding your grass species.
Or just throw out some seeds and have a cup of tea