Dots per inch Is relatively straight forward. If myMarquee is 7x32 and I was 300 DPI I would need a resolution of 2100x9600.I get that.
I was under the impression you could use existing art for a marquee or other smaller parts.
Im going to over simplify, as to not overwhelm.
Raster = dots , vector = lines
When you scale up a raster image in photoshop it polls the pixels. If bi/trilinear filtering is on it "smooths out" the image but makes it blurry. If nearest neighbor is on , it keeps the image blocky. Scaling up a raster rarely results in a good looking image. But if you only adjust the size a little, its not always noticeable.
If you have a vector, it scales up and down without any quality loss. There are no dots to smooth out and lines can scale without loss of quality.
Vectorizing existing art is just drawing lines/shapes overtop of existing art, converting the dots to lines. It is a VERY tedious process to manually, and the results of automated vectoring isn't always good.
Art wont cost you a grand but it can really make a project look protato.
There are tons of high resolution raster art pieces and a ton of vector art for marvel vs Capcom and a ton of marvel stuff in general. There are also tons of artists on deviant that'd love to get hired to do something custom.