1. are all the new parts compatible and are they a good choice? will they last well into the future?
2. is a new power supply necessary?
3. are the new case fans necessary? what is a cpu fan and do i need one for the new build? i'm not sure what to buy, and where to install them
More about :bought geforce 670 windows install crashes
Indeed, the new motherboard and CPU doesn't fit together...
however, the "technician" is wrong for saying that the motherboard is too weak! Also when I see what he recommended (motherboard & CPU), to me spells pseudo-technician (that is why I wrote it in caveats)...
The motherboard has nothing to do with "strength to support the GPU"; that statement is out of place...
if he said that the CPU is not up to the task to service the GPU, than he could have a correct argument;
so my answers:
1) No they are not compatible; on their own, they are good choices, but unfortunately they don't fit together; you'll have to find more suitable combination (change either the motherboard or the CPU); the proposed motherboard from amuffin is a good choice, though I would also check the Asus and Asrock as well; also if you chose to go with 2600K, search for a overclocking friendly motherboard - it will be shame not to overclock that 2600K
future? that is a difficult one when buying computers (hardware);
2) Most likely the cause for install to crash was that the old PSU was some rubbish; But the new one is very good one and if you can afford it, you should not hesitate; though for your setup is a bit of overkill... I have the previous version of that one and it serves me well for 4+ years and it drives overclocked system (check the specs in my profile)
3) No, but is highly advisable! More fans > more airflow > better cooling > longer component life... ut if you overclock, more fans are must!
So in general, you still have some work to do around that computer...