It sounds like you are serious about this and have some money to spend on it. I would recomend reading a bunch of build threads. You want to get a firm picture of what your end goal is. If you don't you will spend money on mods and then more money latter to upgrade them. Many people spend alot of money on their first truck learning and then sell things at a loss to rebuild it. For example if you get duel stock cases now when you upgrade to 4.7 rear case you will want 23 spline and will have to buy a new coupler for your adapter. Little things like this add up quickly.
Right now the best investments you could make would be a welder and a torch or plasma cutter.
As for the truck getting a duel case set up with 23 spline 4.7 in the rear would be safe upgrade as you will eventualy do this anyway. It sounds like this is not a daily driver so weld the rear gears and get some used 31"-33" mud tires. This set up will take you 99% of the places you want to go.
How many miles on the motor. Check the compression and valve clearance and carb. If you buy a new motor now you will regret it latter if you want more power and decide to do a motor swap.
As for bigger things like axles, gears, and lockers once you have decided what you want look for used axles already built. Toyota axles are not great for holding their value and if you wait for a deal you can get what you want used for half of what it would cost new.
