The PSU generally comes with more than enough cabling of the proper connector types for any but the most extreme setups (lots of HDDs, custom water cooling, RGB madness). Even the fully modular setups come with way more cables than you'll likely use. The case will provide all of it's own internal connections for power light, power button, usb headers, etc. You MAY need a SATA cable or two, but most mobos ship with one or two. Cabling is dead simple nowadays and if you have the ability not to put a round peg in a square hole then you are set.
Routing the cables internally is the only hassle, and again most case manufactureres have cable management solutions built in. Routing holes for behind the mobo, wire arrestors to keep things managed, etc. Couple small zip ties and phillips head screw driver is all you need to go from a pile of UPS boxes to surfing porn.