i’m also creating new beds on top of a lawn of creeping buttercup. it’s good to read that it’s an indicator of fertile soil, albeit clayey, wet and compacted!
i am weeding every week and am shocked at how quickly it grows through 5-8″s of muck but i am just remembering that i have to persevere. it seems like the trick of no-dig is to weed your little heart out for the first few months and then you suddenly don’t have to anymore because you’ve won!
we don’t have buttercup on our old site but there we conquered the couch grass and sheeps sorrel now and only have to deal with blown-in seeds which is easy (as long as you never let them establish or seed)