Exciting times, and lots of work ahead of you (but fun work!). As for the fan screws, don't worry about it as the case comes with 12 black fan screws to match the case. As for your cables: I don't know what PSU you have (assuming SF600) but if the cables are hard to move around I'd suggest you pickup a cheap heat gun (hairdryer might even work). You'll probably burn the tips of your fingers, but that's the type sacrifice you have to make at least once to organize your cables.
Lastly, I thought I'd add that the S401 has 6 built-in zip tie mount points. I don't think I've talked about this before but looking down at the mainboard, there are 3 points to the right of the mainboard and 3 along the bottom. I'm including 4 zip ties with each case so you don't have to go out and buy them unless you mess up and have to cut & remove them. Picture below.