I just did exactly that - I upgraded from a Gigabyte GA-Z68MA-D2H-B3 with a Core i5-2500 CPU to an MSI H97M-G43 with a Core i5-4590S CPU. I transferred the same RAM (I was luckily that my RAM was on MSI's compatibility list for my new motherboard), and my PSU just happened to be "Haswell-ready", but only because I had to replace it a few months ago.
Best option? Pick something that's listed in the Buyer's Guide so you know it has been tested by tonymacx86 & the "crew" - there are plenty of motherboards from Gigabyte, Asus, MSI, and ASRock to choose from.
As far as upgrading OS X, I didn't have to because I was already running Yosemite on my old hardware. Here are the steps I had to perform to get my existing OS X installation to boot on the new hardware, as best as I can remember:
Set the proper settings in my new motherboard's UEFI BIOS (in my case the important ones were to disable VT-D and MSR Config Lock).
Remove /S/L/E/GenericUSBXHCI.kext - I don't need it anymore since the USB 3.0 ports on my new motherboard are provided by the Intel H97 chipset (rather than a 3rd party chipset).
Remove /Extra/SSDT.aml (the Haswell processor doesn't need it to "find" its P-states).
Remove the following lines from /Extra/org.chameleon.Boot.plist: