1. On the welded repairs, my assumption is... the repair should be etched and bondo/skimmed and primed. Or, should it be primed before bondo?

Answer to ? 1: You can spray PPG's DPLF - Primer sealer over your welded and grinded body repair first , then continue to do your bondo/plastic work over the DPLF.( with a light scuffing of the sealer before applying the bondo.
Making sure you wipe with PPG's DX 330 or DX 440 wax and grease remover for a clean surface , before spray of the DPLF sealer.

2. Etching Primers...I assume you must use a different etching primer on the Aluminum and Steel, or do you use a chemical etcher (for the specific metal) and prime with the same primer.

Answer to ? 2: Using PPG's DPLF Sealer ( comes in several colors of your choice ) is all you will need for a quality Sealer for all substraits.
But you will need to use PPG's DX 503 Aluminum Conditioner on the bare aluminum !


3. Hi-Build Primer... Once the bare spots are primed as above, can one kind of Hi-build primer be used?

Answer to ? 3 : Use PPG's K-36 or NCP 271 corrosion resistant primer for using over all your repairs, these are both High solid/ High build primers. They also sand easy , but will need retarders or slow reducers as they have
a quick pot life. Meaning they will harden in your gun if let sit in high temps.

4. Color Sand... I plan on color sanding, with rattle can, after the hi-build. Do I need to prime again afterwards, can I used pretty much any kind of rattle can (enamel or Krylon)?
Answer to ? 4 : Stick with PPG products as they are designed to be all compatiable with each other, rattle can products will never give you good results! Use the primers I mentioned above !

5. Will the heat be a factor?
Answer to ? 5 : Heat will be a big factor as with each 10 deg. increase above the recommended spray temp looses about 10-15 degrees of how long a product stays useable.

Lastly and this is as important as the others,
I plan on buying all the products myself, so I know what goes on the vehicle. Know I will be using PPG Deltron BC/CC and the Temp is 115+, what are all the product that I need (with PPG #, if not asking too much)

If you use PPG's DBU base , it will dry alot faster even using the slower reducers in hot weather , as the reducer is a reactive reducer , it acts liks a hardner. It will eventually turn to Jello when it kicks .
If you are going to use PPG's DBU you will have a easier time with spraying as it lays wetter a while longer and doesnt use a reactive reducer for spraying .

PPG has a couple of clears DCU 2002 or DCU 2055 you might check with where you are buying the PPG products for which clear will work best for you , I think they also have an extender that you can add to the clear to make it last longer / make it dry slower while spraying in higher heats.
I use PPG's Global Clear over my DBU at work , and havent sprayed or kept up with the DCU line of clears.

Etching
Etching Primer : PPG's DPLF Primer sealer for bare steel and conditioned and preped aluminum.
This is also a excellent sealer to spray over every panel before spraying color and clear, so
You only need 1 sealer.
Hi-Build Primer : Use K-36 or NCP 271 Fast build and easy sanding .
Regular Primer? : Dont need any other primers if using 1 of the above mentioned.
Base : PPG's DBU with a slow drying reducer
Clear : DCU 2002 or DCU 2055
Reducers The DBC base and DCU Clears use the same DT reducers .
etc.
You can go here and look around PPG's site for these products I mentioned , to enlighten your self on the Deltron line.

http://www.ppg.com/cr-refinish/phase1/frmHome.asp

SprayTech