Prioritize on the steering box area reinforcement, and the bigger axles. Transmission swap at the same time or shortly thereafter. These are the things that can leave you stranded hardcore in the middle of nowhere, so fix them before they have the chance to pull a fast one on you.
Do upgraded lighting, gotta be able to see where you're going. If headlights don't already run off relays, make it happen.
That truck is hydroboosted from the factory, right? Then it should already have pretty decent brakes, even better with axle swap cause of new larger brakes. So skip the rear discs unless they are of the type that uses 3/4-ton front calipers, the Eldo calipers are horrible. Problem is with the 3/4-ton calipers you lose your parking brake, kinda important with a handshaker trans. Look into a driveline e-brake setup to remedy that situation. But really, if you're running low on time, skip brakes upgrades for now.
Skip pulling the engine out too, if she has good oil pressure run her. Loose bearings will show as low oil pressure. Changing the oil pump for the sake of changing it seems a waste of time and efforts.
Get the front bumper first, winch is more important than fuel holder and spare carrier. Do rear if you have time before the trip, but don't delay trip if you don't have a fancy rear bumper, just toss the stuff inside and head out.
Do roof rack if time allows it. Don't waste time on an awning if trip is coming up soon, umbrellas for deck table sets will work nearly as good and are already available on short notice.
Consider replacing the engine fan clutch with something heavy-duty, especially if venturing out in deserts and such. Or add electric pusher fan to help what you have now if need arises.