Either SB or eBates can be used. Both of them technically do not credit for gift card purchases, it's always possible that your order might slip through and get credited. If you add a small item in addition to your GC order, you increase your chances of success through eBates. I'm not sure if it works with SB also.
It depends on whether GC purchases on ebay are one of the categories included for credit. I know that ebates currently credit 1%.
Again, you can go through either rewards program to make your purchase. If it automatically credits, great. If it doesn't, you probably won't get anywhere by submitting a trouble ticket since both programs exclude GC purchases from credit.
As for the rulers, you purchase them each time that you shop at Target for a GC, when going through a rewards program. It doesn't have to be a ruler. Other office supplies like tape, glue, colored pencils, etc. work just as well.
Nice job! What a great feeling it must have been to be able to take such a nice trip and know that part of it was free!