Pure soil wouldn't be a good option. Anything that's subject to high traffic, whether foot or vehicular, will also be subject to soil compaction which implies w

Pure soil wouldn't be a good option. Anything that's subject to high traffic, whether foot or vehicular, will also be subject to soil compaction which implies water pooling. That's a long way of saying those parking lots will turn into mud lots. At a minimum you could grade and gravel them, going the extra mile to crush the gravel so it stays in place longer. I do this with the driveway at my house because it rains a lot where I live. Paving would arguably last a lot longer and probably be more bang for my buck, but not having a place for water to go and having a basement is not a good combination. On my driveway we only tend to get clovers and really resilient weeds. So, either really shallow rooted plants or weeds with absurdly strong roots. You're not likely to get native plans to grow unless you section off parts of the area for maintaining living soil.