Looks like a wandering gnome said pretty much everything I wanted to say on the subject. What I'd recommend is on the highest difficulty (Commander plus) use a modified version of Attunement. You get the full effect of three magic items only and can attune after a long rest. Maybe have some unattuned bonuses that are much less busted so itemisation doesn't feel too unsatisfying. I'd also agree with preventing martials using scrolls because that's another way you can stop the game getting too easy. If you add a challenge mode I think I'd run at least three martials as it stands.
