I know its a bit of search but looking through all the build threads will get you the most info.
As far as fussing, yes fuss the A/C side. And fusses between power supply & drivers is good also. Size/amps, all depends on what your running. Also no fusses between servo's/steppers & driver, just hard wired there.
The enclosure a few main points to go by.
One, mount your drivers so the wire feeds can be as short as possible to the power supply. DOnt daisy chain them.
Two, you need to think about when you have to tune the drivers so they will need to be so you can get to there ajustments unless it is all software controlled.
Three, BOB, addon cards such as spindle controls, MPG hookups, Smoothstepper,ect,ect need to be mounted so you can get the input hookups to the outside of your inclosure. If they use cables then mounting them so the cables/connectors going to the face of the controller are as short as possible.
Four, you need to keep power harnesses seperated from logic wires/controls.
Five, make a grounding point on the case somewhere so you can ground all parts of the electronics to one point. This is called a star grounding point and you can do a search and find a lot of info about it.
Six, always use shielded wiring for power, or logic hookups. There are probably some parts you could get buy without shielded wiring but its best to use it everywhere you can. If you do use some wiring that is not bundled and there is more than one twist them together so it will help fight off noise interferance. Wires twisted together kinda create a shield of sort.
Seven, always expect to be wanting to add on later. If its your first build yuo will learn more about what you want & need so leaving room for extra's down the road will be good.
I am sure there is other things to consider but this should be a good start on your research. The pics of my enclosure are not the way it is layed out anymore and I dont have a way to provide pics to show the changes. Maybe others will have some pics to help.