I am trying to print a number of my paintings/drawings to stock for markets and I'm having a world of trouble with any of the shops I contact.

1.) They don't seem to know what I mean when I request an "art print", so I've specified that I just mean matte medium weight paper (should I be including other specifics?). Most companies I've found seem to do documents, not art, and want me to send it as a PDF which would be more work for me.

2.) They've also confused me about the quality and size of my scans. I don't quite understand the physical painting -> scan -> digital image -> printed painting workflow enough to fully operate it correctly. My scans are at 300 dpi. The originals are all abnormal sizes though for printing (Aspect ratios are 3:4 and 1:2 as an example). I don't want to crop any of the original out to get a more standard size (I'll likely change the ratios of my originals going forward now that I know how painful abnormal ones are to deal with), and I would like to shrink/enlarge the prints from the original size. I did crop the scans as close to the original size as I could get it, but the dimensions on the file don't seem to be correct bc they're odd numbers. One shop told me I would need to size the digital file to the printed size I wanted to be sure the quality is retained. I think I know how to do that through the software I use (Krita), but I don't understand why me doing it would be different from them doing it if the scan is 300 dpi.

3.) I also wanted margins on the prints, which are not on the scans, one shop told me that I need to add a bleed to the scans in order for the print to have the margin. I have no idea how to do that. Friends who understand printing far better than i do also said that doesn't make sense. Is this just a bad print shop, or should I be leaving the margins I want on the scans?

I'd appreciate any advice anyone has on requesting art quality prints, sending the files, and getting the scans into the correct form/specifics for it to be easily printed. I have gotten so frustrated and confused through this process, it's been over a month since I contacted the first shop and I've gotten no prints done. I have cried in frustration. What am I doing wrong?