Hi Mark,
1. After I've media blasted and I'm going to be going to primer/paint within days I do not wipe them down with any metal prep. I do hang them and blow them off while I run a tack cloth in front of it. I make sure to blow pretty much every square inch while wiping it down with the cloth. This actually sounds time consuming, but goes very quickly. If they were to sit around for weeks then I might wipe them down with DX330 and repeat the same steps above after that.
2. If you spray PPG's DP line of epoxy primer I believe you have 72 hours to shoot the topcoat (the paint) without sanding. Once you pass that 72 hour threshold then you have to scuff up the primer with a scotch brite pad or fine sand paper to get a mechanical bond between the paint and primer. If you shoot the topcoat within the 72 hour window the DP primers are designed to chemically bond/x-link to the topcoat....no sanding required. I usually shoot the paint an hour after I spray the primer.
If you have pitted parts and need to sand that is a totally different story.....I spray 1 coat of epoxy primer and then shoot 2 coats of sandable ureathane primer an hour later. Then next day the sanding begins, sometimes several coats of sandable primer are required, and sanded out or filler. After your done with your body work (whatever is required) I usally shoot a coat of epoxy over the top prior to paint, you can even do that after wet sanding right before you paint.
3. I have enough land where it is not an issue, but my I can paint the trees about 30 feet away

Also, my neighbors a few acres away can always tell when I'm painting by the smell ;p I initially set up my booth so I could slide in replaceable airfilters on the inside, in fact I think in the pics you can see each opening.....each opening take 3 filters. The problem I had is that the filters fill up with overspray fairly quickly. It's a little tougher on the fan and stuff because the blades build up with overspray, but I don't have to keep changing filters constantly now. If the overspray builds up on the fan to much I'll just start chipping the big stuff off. But, if you have cars a few feet away.....you may have a problem and might have to filter it. You might also want to design it similiar to mine, but then have the fan on the top of the plenum and vent vertically out the roof????
Hope this helps and sorry about the late reply....was up in the woods for 4 days at my hunting cabin deer hunting, just got back this evening......
Matt