It's a paper texture so it can't be repeated easily without it looking awful.
Most sites that use paper texture backgrounds manage to use a tile (maybe not for the top or the edges if they are one-offs).
Gimp has a "make into a pattern" tool, so surely Photohop has that too.
If the image has more than 256 colours, you'll think twice about saving as PNG, simply because it's lossless. If it were under that number you could index it and have a smaller 8-bit PNG compared to jpg, but jpg's being lossy are usually smaller for textured and photographic images. You could play more with the jpg quality, while keeping a png of the original (since every time you save the jpg you lose a lot of data), until you see the worst quality you're willing to put up with, to lower the filesize. You should also have an option like remove comments, EXIF data, etc. Why have the file bloat with all that junk?
What i want to know is what is the best way to load this image. Having the image in 1 file could take a few seconds to download. Would it be better to cut the image up into maybe 9 square pieces and then have a 3x3 grid using divs each with a separate image?
So you know, you'll always have slower reaction with multiple files over one file, since each file needs to spend request time between browser and server.
There's also Cicada Principle, if you can figure out how to mimic a paper texture with that... looking at the "Koi" example you could maybe do any unique top or edge images you need.
This does have the disadvantage of multiple files, files with transparency (which are larger than flat files), and doesn't work on older browsers (this uses the CSS3 multiple backgrounds property), but if it means it's the only way to get the background you need and each of the individual files are still relatively tiny... might be worth it.
A single 100kb image will load faster than 10 10kb images
but a single 100kb image could (depending on client bandwidth or your server speed) be slower than 3 files of 10kb each. So I'd only even think of multiple images when the total filesize is also much smaller than your single image, to make up for those extra server requests.