If you want to know how Ford did it, but a set of factory assembly manuals.  They were invaluable in putting my car back together, which prior to my ownership had likely been striped down for use as a race car, and then hastily, and incorrectly, reassembled to sell it.  I dealt with missing parts, incorrect hardware, etc. as I began to restore the car back to factory stock condition.  The assembly manual, once they became available, cleared up what I wasn't sure about, showed me where clips, etc. went (many of which were missing), showed correct routing for lines, wiring, etc.  They are not cheap, but they are invaluable tools.  

By and large, and factory insulation was installed first.  Then fuel and brake lines were some of the first things to be installed, followed by wiring.  

The insulation is definitely supposed to be under the heater box/AC unit.  

The dash vents mount, IIRC, as follows:  The center vent is secured by a stud that goes through it and the dash frame from in instrument bezel on the right side, and one from the trim piece on the left.  The side vents mount with screws at the top, and nuts/bolts at the bottom (or maybe they are supposed to be screws and nut clips, as access to the nuts in very tough (I made a tool for this)).  

 The Jim Osborn assemble manuals will make life much easier. It lets you know routing and how it should go together…. It won't tell you when it should go in though. There were a lot of things that I installed more than once cause it interfered with something that I thought should go in later. For 1 and 2-Working under the dash, have all paint work done, add whatever spray on or peel and stick insulation or you might want to use, then install the factory type insulation pad. Cut what you need when you need. Installing stuff, start at the top and work down-wiper arms and motor, pedal assemble, steering column without steering wheel. It's amazing how much working room the steering wheel consumes.3 Column, gear box, and any hoses prior to hydroboost. You can install the motor to help make sure of avoiding any of its space. It doesn’t have to be a complete motor. Use the trans, block, head, valve cover and header/exhaust manifold for that side. Then you can take it back out for working room.4 Start thinking about the wiring now. Are you using a factory harness, aftermarket harness, do you want more circuits than either of them provide for upgrades? Stereo equipment? Power windows, seats, an extra USB or USBC port for charging devices? 3G alternator upgrade/removal of factory voltage regulator? Horn relays? Headlight relays? Wiring under the dash will have points it can be attached to the body. Tie wrapping it together should be sufficient. Keep the tie wraps loose cause there will be another wire that has to go that way. McMaster Carr sells the wiring loom that’s most cost effective to purchase than going through Summit. https://www.mcmaster.com/products/wire-looms/wraparound-wire-sleeving~~/?s=fabric+wire+looms5 Dash pad at the end. Wiring can be routed prior to AC and defroster ducting install. Terminations can be afterwards.6 This is where the Osborn assembly manuals help out with all kinds of pictures and exploded views. My car was in a stage of disassemble from 1988 to 2012. I bet I have 500 pictures. They were never what I needed to see!! The manuals were much more helpful.