I actually have a back-log of scanned stories that people have sent in and I haven't had a chance to work through them yet. So it's best to hold off for a bit.
Bigger is better, because then I can do any necessary clean up and stuff before shrinking the pages down. I don't have RAR. Send a page at a time.
But if you're a photshop pro and know what you're doing and can get the pages in final presentation format, actual size submissions would be easier.
But make sure I like the story first, otherwise I really don't have much motivation to spend time on adding it to the site. And too much bad stuff will dilute what's already online.