If you decide to buy a HB SLI bridge just be sure to get the one with the right spacing for your motherboard and where the two cards are placed in it. I don't know what the correct spacing for your board is, but as an example, on my FTW K board the two PCI-E slots designed to be used for SLI require the 2-slot spacing.
I wouldn't worry too much about the SLI bridge. Just put the EVGA one on auto-notify and pick it up eventually when it becomes available again. There's really no rush, since the benefits you see with it will be modest.
I'm glad you're learning a lot here. That's the way to go. If you keep at it, when it comes time to upgrade your system you'll be able to make informed choices and pick the right gear for what you want. For now your machine will be fine, even if you might have done a little better with some of the choices. It's certainly a pretty rocking machine, whatever else might be said about it.