I think you need to keep things simple to try this technique. Once you’ve mastered it then you can start adding in other flours like rye and buckwheat. Why not try a mix of wholewheat and bread flour? If you really don’t wish to use bread flour then keep it 100% whole wheat. If you wish to try it then don’t rush into it before having a plan on how your going to tackle this sweet levain build. Forkish builds a lot in excess and it can be wasteful. Also the flours you’re using might not translate perfectly to his recipe given. I was just showing you how a starter or levain can be maintained and fed to produce different results.
If you haven’t started another loaf yet we can come up with a recipe for you to try.
I spread the folds out as evenly as I can through the bulk ferment. But there’s not much point in folding until it has relaxed.