Likewise - though the kid hasn't had an actual overnight backpack yet (it's been either day hikes or car camping), and he's 10. I'm not sure what kind of advice you're looking for. You obviously already know how to mix formula and give it to the kid.
Things I might be thinking about in your shoes:
1) stove system. Warm (body-temperature) milk is recommended, and on cold nights rather important, compared to streamwater-cold milk. You want a stove, a backup stove for overnights, and a big pot that your bottle fits in easily.
2) water supply. You don't necessarily have to boil the water before mixing, but I'd use a good filter. Giardia in an infant would get pretty serious.
3) bottle hygiene. If you're not already using those collapsible plastic bags, try them. They get way less air into them (cause less burping) than conventional bottles, and they take almost no pack space, so you can bring lots. Treat them as disposable (but carry out) - don't bother trying to get them thoroughly clean after use, at least until you get home. Change nipples at least as often as you normally would, and carry a few extra for when one inevitably falls into the mud. (Ditto extra pacifiers, times a thousand.)
And of course, have plenty of tightly-sealing waste bags for carrying out diapers.