Get it running, fix all the safety stuff like brakes, seat bolted down ect. Then check all the wiring and fuel lines, you don't want it burning to the ground. I would fix it as you go, you will love driving it. That's what I like. I do one major thing every year.
Have fun, nice truck. I love the K20s. Get a fleetside/styleside bed, it keeps the lines clean from the nose to the tail.