Hi, DuttPanda! I am more than happy to help you any way I can.
1. Do you mean you want the background of the table to be a rendered image? Yes, that's possible. I don't like external links, myself, so save the image (ie, goku_render_by_aliensurxx.png) and upload it to your wiki. Open the page the table is on, and, on line one, delete the background-color:#C1B791; value, add the background-image:goku_render_by_aliensurxx.png; value, and change the background-position:1% 25%; to background-position:center; and you should be good to go.
2. No and yes. The images can be any size you want, as long as they fit within the table and remain cohesive. While I usually design everything at 600px, the table we are talking about has an inside content dimension of 640px. I usually allow a few pixels for borders (and/or cellspacing if it's value isn't set at "0"), but it's not required. The top two images are just centered images set at the size they need to be for the font used to be visually aesthetic when juxtaposed to the images below. The next four images are spaced at 160px a piece, equally out to 640px. The number and size of images can be customized, as long as they fit the table space providged (otherwise causing an unsightly line of text running out of the table and, sometimes, off of the screen). The five buttons at the bottom are only 110px apiece, equally only 550px, but they are spread out so that there is approximately 22 pixels in between each one, leaving them centered below the images above. Those can be also be customized with any sized image, as long as it fits the table.
3. I have no problem becoming a temporary admin, although most of the CSS tweaks you need (unless you want to change overall font colors and sizes, button styles, etc.) can usually be done directly on the table itself. By "navigation bar", are you talking about the links table you are working on, or the wiki's top-most menu? I like the way the Far Cry wiki used the Far Cry logos in it's top-most menu, and you already have added links, so imagery should be no problem to add (in lieu of the links). I could do it for you, or, as I know you, like most people, myself include, would rather do it yourself, I could just help show you the way. The choice is yours. No matter what we are all here for you! The rest of the wiki looks great, though, you're doing a terrific job!