The armor [...] also expands to cover your entire body, although you can retract or deploy the helmet [...]
At level 9, you gain the Armor Modifications feature (TCoE, p. 17), which allows you to infuse multiple parts of the armor (chest, boots, helmet, and weapon).
So, before I get to level 9, can I wear magical boots and/or gloves? Or does my armor cover my hands and feet in such a way that I can't? Same for a magical helmet: can I wear one while my Arcane Armor helmet is retracted?
After I reach level 9, can I infuse (or find) a pair of gloves and put them on? Gloves aren't in the list of separate infusable armor parts. Can I find a pair of boots that aren't infusions and wear them?
I am assuming that when my armor covers my entire body, that's just for flavor, rather than a way to prevent me from being too awesome, and that the separate infusable parts are more for convenience ... but you never know.