A bit of a belated reply, but I'm an artist that uses Redbubble, which is another (more merchandise-oriented) POD site. My work is digital, so I don't have much experience taking product photos, but it is my understanding that a good camera and a homemade light box/some extra photography lights are really all you need to take good product photos. For actual print reproductions, though, you may want to look into professional scanning and the like at a local print shop, the kind that does giclee prints and the like--it's a bit expensive, but especially for fine art prints, you want a really high DPI and the quality difference can be pretty noticeable at larger sizes (unless you're a *really* good photographer who knows what they're doing).
The other thing to consider is promoting the work once it's up--handing out business cards at car shows is a good start, but these days it's all about the social media, which may not be a time investment you or your father wants to make. Putting up new work consistently on Facebook, Instagram, or elsewhere, letting people know which shows you're going to be at, promoting your cool new prints or products, etc ... it's definitely a hustle. Though since it sounds like your father has an established client base, it may be easier to start a mailing list--that would get you most of the way there without having to navigate multiple social media accounts. From there, advertising at the car shows (and offering limited commission slots versus directing them towards the POD for open edition prints) might work.
Hope this helps!