In order to "upgrade" the CPU, you would need to swap mobo's around aswell, as your Ivy Bridge 2500K runs socket 1156 while the latest Haswell runs socket 1150 - so no, not a major super duper woohoo upgrade and a tad costly for a very minor performance gain in regard to gaming (you'd be much better off OC'ing the 2500K on your current mobo
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For headsets.. it's really what you like. The big difference is when it comes to USB vs. Traditional 3.5mm minijack plugged ones.
Coz I'm a techgeek, I prefer USB headsets since they convert the mic signal to digital inside the left earmuff meaning there's VERY little chance of picking up a lot of eletronic static on the way in comparison to minijacked headsets who had to run the long wire to the plugs on the back of the PC (or front).
Higher quality headsets ofc have higher quality shielded cables n whatnot, but still.
There's also the headset w. mic vs. speakers + external table (or boom) mic discussion - Imho it also breaks down to how much noise you want in your environment - parents/flatmates/significant others complaining about the speaker sound - in these cases it'll be safer with a headset for sound out.
Sound recording is another matter. My usual complaint with headset mic's is that they're prone to picking up a lot of "air" - we've all heard "that guy" on TS/Vent/Mumble/Raidcall who just can't adjust his mic to NOT pick up his mouthbreathing n whatnot. A table/boom mic can be placed further away so it won't be in the airstream, yet still pick up your voice.
I use a cheapskate $10 Logitech analogue tablemic (although it IS kindda stereo-balanced) alongside my speakers and I have no troubles getting a decent signal, noiseless and clear, recorded.
In regards to a soundcard - you're better off spending good money on a mic than a seperate soundcard, imho.
If you wanna buy a big 7.1 USB Digital Headset, you go for that aswell!
