Plywood, due to its construction, is far more stable than solid wood. So in that sense it shouldn't be a problem. Hard for me to believe that you're seeing single-digit humidity unless you live in a desert. Even then, you should be fine as long as the wood is acclimated to your conditions before you start building. If you get huge seasonal swings in humidity, that may be rough but it can be dealt with.
Using an oil-based product doesn't add any moisture to the wood. Even a water-based product doesn't really add any moisture to the wood. Once the finish is cured, it's done; you don't have to do anything else with it.
FYI, most stains are oil-based unless they specifically say that they're water-based. Water-based products dry so quickly that they're difficult to work with. Which makes them especially difficult for stains, where you typically wipe the stain on, wait, then wipe off. If you're using maple, I would try to avoid staining entirely! I'd try to find an oil-based clearcoat and use that. The oil is amber in color and thus will give the maple and amber tint. You can use TransTint dyes to change the color of the clearcoat. Adding dye to a clearcoat creates something called a "toner". You might do this as the first coat, or first and second, then cover it with the clearcoat.
Unfortunately, one of the downsides to an oil-based clearcoat is that it takes forever to dry. And while it's drying any bit of dust, hair, or junk that touches it will end up embedded in your finish! If your workshop is dusty, like mine, you may find that a brushing an oil clearcoat onto your cabinet is tricky business. Wipe-on finishes dry much faster, but require more coats to build up the same level of coverage. Water-based products also dry very quickly. Sadly, this means that they're more susceptible to brush marks. And they often add an unpleasant blue- or gray-ish cast to the wood.
Whatever you do make sure you experiment with the stains, dyes, and clearcoats you plan to use on pieces of scrap wood before you start on your cabinet! Do to the scrap wood exactly what you're planning to do to the cabinet. If it turns out looking like crap, you've only ruined a piece of scrap not the cabinet you've spent days or weeks building!