I'm not currently planning on any crossfire configuration (for now I believe my 7970 is good enough) but for future purpose, is it better to go for dual or should I shell out more than $100 more for a 4-way crossfire board? Can this board handle 3-way? Does 3-way even matter? Thanks a lot.
Not unless you multi-monitor gaming, 3D, or using midrange cards, but since you're starting out with 2 top of the line cards, but the time 2x7970 won't max out a games you'll probably find it most cost effective just to get a new card (and whatever motherboard and cpu is current at the time)
If you aren't ever going to do eyefinity/NVIDIA surround, then you will almost never need more than 1 7970/GTX 680 unless you are intentionally beating what it can do (trying to play Metro 2033 with ultra settings+max AA+tessalation etc). The only thing that Xfire/SLi is good for is multi-monitor gaming, setting record benchmarks, or playing said settings which is really unnecessary for most. Dual 7970s will meet all of your needs for single monitor gaming. If you are looking to pass dual Xfire/SLi I would recommend looking into the X79 chipset as it natively offers 40 lanes of PCI-e, making 3-way and 4-way configurations extremely easy to do.
2x 7970's for 5760x1080 eyefinity, I can run pretty much every game on Max settings flawless 60fps+
exceptions are Metro 2033 with tesselation still runs playable, but you can tell its under a lot of stress
but things like BF3, Borderlands2, Mech warrior online, Guild wars2 all maxed out no problem what so ever