Hi Jordan,
That sounds like an epic adventure, and that’s the type of trip packrafts are made for! I’d use single-person packrafts with airtight zippers for internal storage… However, I strongly urge you to gain lots of moving-water experience and take a swift-water rescue course before venturing out on a remote, multi-day river trip. There’s no room for mistakes when help is many hours or days away.
On most rivers, paddling speed is largely determined by the current, so I would concentrate on other factors when choosing a boat.