I used Word on my phone to edit a word document the other day, it was fine. I doubt MS have left the slightly different version of Android on Chromebooks too far behind.
I think the free Office apps only view, you need a Home/Pro sub to edit. But there's probably a cheap student edition if you don't already have one.
Yes, I assumed we’d buy him a home/individual/student 365 suite if needed, though from what I can tell we wouldn’t need it for his actual school work, only if he wanted to start typing his school assignments (though I think they’d mostly be handwritten as school handwriting and the use of cursive is still a *big thing*).
My granddaughter's now in Year 10 and has only ever needed a Chromebook for all her school work. It's mainly been for homework, much of which is web based and there's been no need for access to any Microsoft apps, so we've never tried the Chrome compatible versions. We bought her a mid-range model three or four years ago and it's been perfectly adequate, so I don't think there's any need to splash out on a top-of-the-range model.