I have never used google to store image files before, but I do believe that the webhosting that I am using for the plugin has enough space(it has 10gb of space) and bandwidth(it has 100gb of monthly bandwidth, and since your sets current combined total size including images is about 120mb, we can have over 800 complete downloads a month) to store all the images, it could be set as a backup source in the case that the Wiki has problems.
Additionally, before I start making the CardImageURLs files and/or the webhosted image database I should ask what the names of the images will be in the sets. Using the card number in the set is a good option, it's also what Magic's plugin does, but it may be easier to just use a replace function on the excel sheet. I'll wait until you decide which one to do and I'll follow suit.
Also I've sent you a PM including the webhosting's location, login password, login email, yatta yatta because I never know when I'll be unable to update it or randomly hit by a car and put in to a coma. ;P
The Wiki also contains the japanese and english version of the first few sets, so I guess a "Japanese" quality setting could be added, since the japanese scans are of higher quality but obviously not readable.
Edits are in bold