I think going 312mm is a no brainer, I'm thinking about doing to my A4 as I don't think the standard size discs are that great compared to the 312 on my Golf..
Do it now as the cost isn't that much more on top of the new pads, hoses, discs and fluid. I wouldn't bother with the VRS calipers, save your money for the suspension mods.
Can't you find any secondhand carriers cheaper?