So we don’t know how many moons there are for sure, but if the rumors are true there will be a lot. I think any% will be a reasonable time but 100% may just be a long boring grind. Thoughts?

I mean even if it's a lot the main thing will be how quickly each star can be collected (which will obviously vary) and the mechanics needed to pull it off. I hope that it isn't too long but honestly even if it takes around 6-12 hours I'd probably give it a couple of attempts during my days off. Any longer than that though I don't think it would be worth it. Maybe we could have some zone% runs if it does take far too long?

That could work. And there will always be that one crazy guy who does a 30 hour speedrun.

No matter how long 100% takes, it will be added, along with all moons (unless all moons is 100%).

odme what if the difference is like, a single shop trip

There's no need to worry about specifics until the game is out.