

I think I have two general responses.
I think you’re right in that photography and the style of photographs has evolved with technology. Each of those technological steps has been partially shaped by art (what makes it to market) and taste (what succeeds in the market). Additionally, darkrooms gave a lot of leeway for the look of the final image. This also ties into what makes for a compelling image - you’re often looking for a dramatic scene, a subject that’s a bit out of the norm, and/or unique lighting. Yeah, there are street photographs of everyday people doing everyday things in normal lighting, but they often aren’t that compelling.
In other words, photography is often stylized. I personally think that’s OK, especially when you consider how flat lightly processed photos are.
The good news in today’s world: if you shoot digital you can shoot raw + jpeg and change the look of the image pretty drastically with non-destructive edits. I’ve re-edited photos I’ve taken over a decade ago and changed their look significantly. I can do the same again in another 10 years if it strikes my fancy.
1 and 5: Either should be fine, especially if the seller is reputable and has reviews. Many sells will have a store on multiple sites, but in some cases people will resell other people’s work. See if you can track down the original creator to support them 2: I suspect everyone will want STLs they won’t have to do any processing on. What do I mean? Well, I could give you a STL for a piece that’s massively too large and would need to be split into pieces or a different STL that will be impossible to print well. I suspect print services won’t want to deal with this, will charge for it, and/or you might not be happy with the final outcome 3: If you’re paying someone to print the parts, they will likely have larger format printers. However, this might cost some $$ 5: It depends how thick the designs are and how strong you want them to be (more perimeters = stronger), but keep in mind that you’re also paying for machine time and potentially processing (eg surface finishing, support removal, etc). To get a feel for a quote without buying this design, find some cosplay armor on something like printables and use that for quotes