Taking the logical approach, decide what your finished vision of the truck is.
Is it a show truck where judges will be looking at the underside?
Do you want it to remain drivable while working on it?
Most all projects that get started realistically don't ever get finished and wind up as a pile of parts on ebay or craigslist. Decide if you really have the commitment and dedication to see this project through, and the finances to carry you there.
You WILL absolutely, 100% take a component off you didn't think you needed to replace, and find out it indeed needs to be replaced. The more you pull off, the more of those components there will be.
I say that because you mentioned wanting to keep costs down. I assume you're not made of money (none of us are!!!) so anything you take off becomes a potential cost when putting it back on, especially if you're replacing with aftermarket parts and find that the piece you thought you could salvage just doesn't jive with the aftermarket parts you've already purchased.
Another thing is don't purchase things ahead of time, so far that you can't return them. I had this happen where I bought a part, then a year later finally try to install it and it doesn't work, or it's non-functioning and I'm stuck eating the cost.
Instead of trying to save time by pulling the body AND doing the frame, decide which NEEDS to be done first, and keep the truck as intact as possible to avoid discouragement and overwhelming parts cost.
Most of all... HAVE FUN!!!!!
