I can answer a few of these. Essentially, I'd be more careful about flooding the community than ruining the site infrastructure.
>Or is your site smart enough that it uses the first to use as a host for the second file?
Tinyboard and children (like this site) don't. It uses the Unix timestamp of when the post was uploaded as an identifier (in the address).
Usually that duplicate problem is 'solved' by not allowing duplicate files, but leftypol doesn't do that yet.
I know Lynxchan is smarter and uses a hash of the image (those 'random' letters and numbers) as an identifier, which is always the same for exact duplicate images.
.gif (I posted that on two different boards, same link)
>1) Does people posting many images cost the website a lot of money?
Most server hosting deals work on a flat rate IIRC, like 2TB total storage, 100mbps bandwidth, possibly with a total bandwidth cap like 10TB a month. If so, you individually wouldn't be costing money by posting more or less unless you're hosting entire films. Either they need to pay for a whole extra tier, or they don't.
/b/ currently has an average of 12 images per thread, and 36 pages of 10 threads.
If we assume an average of 2MB per image, that's only 8.6 GB of storage needed to host /b/!
Let's assume you either manage to double
the amount of images on /b/, or the average size. Now it's only 17 GB.
If the number of files is a concern, there is an option to add image limits per thread like 4chan does or we could enforce stricter size limits. There are people posting multiple large webm videos at once so you're probably fine unless you're intentionally acting in bad faith or posting full documentaries every day.