I have the same M1 case waiting for a build, and mine arrived at the end of last year. I've also been considering the air vs water options for it.
The i5 should be no problem to cool with air, and the Noctua NH-U9 fits into the M1 easily (from a clearance point of view). I like air cooling from a longevity standpoint, as I keep my PCs for a very long time.
There's also the noise consideration. While some water pumps are barely audible, other can make a thrumming noise which some people don't like. An air cooler, especially a Noctua, with suitable fan control, can run almost completely silently. This is one of the advantages of going overkill on the CPU cooler. You end up stressing it very little, and having a quieter PC.
Most AiOs have a lifespan of around 5-6 years before they need replacing, as the liquid does permeate the tubing over time. While you can refill some of them, it's not something they're designed for.
An AiO will give you headroom to upgrade in the future without needing to buy another CPU cooler. You would start to run into the limits of the NH-U9 with a higher end i7 or i9.
If you do look into an AiO, put the Arctic Liquid Freezer II onto your list of considerations. It's at the top of mine, although it's very difficult to find, especially at the recommended retail price of $99.
Here's a review of it from Gamersnexus:
[MEDIA=youtube]KPaSEGe6ML0[/MEDIA]
