Re: Paint guns.....
I agree, you should use a separate gun for primer. Harbor Freight guns will work fine for that.
For what it's worth, I painted semis for almost 30 years and the last spray gun I bought and used (and loved) was the Devilbiss GTI with several different tips.
The 1.3 is recommended for what your doing. Only requires 25-30 lbs but any HVLP will require a high CFM. Your portable 3 horse compressor is not going to work for painting an entire vehicle. My 5 hp 60 gallon 2 stage won't keep up for an entire vehicle.
For me, the GTI felt and sprayed like my JGA, that was my favorite spray gun for 20 years.
You can pick up a GTI for about $300 and it will do a good job just like the Sata.
2010 XLT 4X4