tatest is spot on. The key is realizing what stuff you -have- to have versus what are options. Realizing it on your first rig purchase, and not your second.
One big question: Will you be in one spot, or moving from place to place? If on the road more, you might consider a used diesel pusher and a toad because they are easier to deal with as opposed to the hitching/unhitching routine. If in one spot, a truck and a fiver would be closer to the idea because there is one less engine/drivetrain that has to be maintained, inspected, licensed, insured, and paid for.