Sasha
Even though you only plan a belt, allow for future options and add 3 foldable D-Rings to the cart. You can't safely predict the future and what choices will be made, particularly by her and/or (overeager) mates, lovers .... Whatever plans may unfold, be prepared to unfold appropriate solutions. Consequentially, if you can easily include cheap but potentially priceless upgrades, do it.
That's what I'd consider reasonable. Admittedly, and as said somewhere, it could also be my controlling, overconcerned(?), (and perhaps just slightly sadistic š) side of me.