Well, here goes:

1) What exactly does the heatshrink do when you sleeve cables?
2) Which case should I get: Tt Kandalf, CM Stacker, or LL PC-V2100 plus (or any other suggestions)
3) What is the best way to get a 150mm fan onto my case?

I'm pretty new to the modding world.

~Toad

1) it heats plastic covering so it shrinks and binds said cables into a round shape.
2) your case = your call
it's mostly a matter of your choices of features and appearance. i reccomend a raidmax, thermaltake, or antec for good quality.
3) depends on the case. i would'nt buy a case where modding was nessesary for fans, but that's just me