It really depends on the specific color. Some of Tamiya's paints are more translucent and are heavily affected by the primer. Others are so opaque that the primer doesn't seem to have any impact. The best thing to do is try the spoon test. Take a white plastic spoon and put white, grey and black primers on it then overcoat with the color of your choice. That way you'll have a side by side comparison and can easily judge which primer works best for your application.
What you have there are parts from 3 different kits & manufacturers. The one on the left with the separate hood is the AMT 53 F100. The one with the flip front is the MPC 53 F100. It looks like the blue one may be the MPC as well. The copper colored parts are from the Revell 56 F100. They are mixed scales as well. The AMT & MPC are 1/25 while the Revell is 1/24 scale. I like your scratch building I'm looking forward to see how this turns out.
I have my doubts about the 41 Woody. The shape along the top edge is more rounded that on the 37. I've been considering a similar conversion myself. I think the Monogram 30 Model A woody might be a better place to start. Also there is a 37 Cabriolet available which should make the job easier too.
Nice build. My daily driver is a 2006 STS-4 so I did much the same as this one. I used the wheels from the Cadillac pickup as they closely matched what i have on my car. i also used the grille from the pickup as I don't have the V version. http://public.fotki.com/KenK/my_models/models_of_11_cars/2006-cadillac-sts/
Aaron, Glad you showed up last night. If you have any questions you can always contact me at: firstname.lastname@example.org I'll be glad to help. Looking forward to seeing you at the next meeting on Feb. 9th. Ken