Thought process is this , buy a cheap sandy combo now and if not satisfied upgrade to Haswell later on . The 2500k will hold on till then I guess , only I wont be able to put 2 graphics card later on because the PCI system of sandy wont support the 3.0 cards.
You can do this but keep in mind that the Intel Haswell chips will be based on the LGA 1150 socket, so no backwards compatibility with current generation motherboards / chipsets. Means shelling out more for Haswell [processor + motherboard] and maybe the RAM [DDR 4].
Also you can go for a multi-GPU setup no problems, I just have a few of my own reservations to avoid them. The current generation(s) of graphics cards display no advantage if they are run on PCIe of the 2.x standard rather than the latest 3.0 standard. It is only if you run these cards on gen1.x PCIe slots that you will hit a performance penalty.
Hope this helps, Cheerio!