Gear towards R9 280X instead of R9 290
Best cards right now are the ones that offer high hash rates at low power consumption and little heat. Basically you're going to want 7950's, R9 280's or 7970's in that order. Make sure you read several reviews of the cards to get a gist of which manufacturer offers a card that functions well- i.e. decent cooling on the card.
I would invest in an i7 4770k right now at the price you can get it for and use it for CPU mining
You're going to need at least a 1200watt PSU (look for 80+ gold certified).. probably even more with 5 cards. I'm not sure how many cards "rabbit" supports.. I've never even heard of rabbit to begin with. But make sure thats an option before you buy more cards than the system can run.
Make sure you buy risers for the cards so you can keep them elevated from the motherboard and separate from each other.. this allows for lots of room for heat dissipation off the cards, rather than having them stacked together. Just google pci/pci-e risers.
You can easily do 2x4GB of ram to begin with, just make sure the pins and timings match the motherboard requirements
Here's a good start for understanding some of the hardware information:
https://litecoin.info/Mining_hardware_comparisonHope that helps/gives you some direction.
