I.C.E Setup!

If you have alot of amps etc then yeah the power cable will matter, you'll want 0G wire, but what your looking at I think you'll be OK at the normal stuff (4, . What youve listed will be good for clarity, just make it a mix of component 5" and 3-way coaxials then some decent tweeters.

you dont have to go with different sizes, just different types imo, the coaxials have the tweeters built in and are normally 3 way, so the mid-range and then 2 types of tweeter built into the centre stem. Then component speakers have full on mid-range with a independent/seperate tweeter - both have their advantages and disadvantages

As for positioning, first off the standard speakers just upgrade them, so its neat, not in the way at all, and solid, then maybe experiment abit, keeping them high and out of the way again, mid-range and bass travels pretty well low as the vibrations are used against the car bodywork aswell, whereas treble struggles to travel in the same way so thats why pillars are a good option (and their small enough of course)