Debatable. A lot of APU cases are designed around using external bricks, whereas with no lp GPU you can mount a variety of PSU inside the L5, and still get cooler clearance to run the L12S. Lots of APU cases force you onto small coolers.
As in not the stock one. I grabbed an ID cooling IS30 I was planning on using a different build but wanted to mount it in my A300, looks like part of the heatsink would hit the small VRM? heatsink that.
There's not really anything janky about them.
On my ASRock board, the 4 pin fan headers are rated for 1A. A single Noctua F12 PWM fan has a max input current of 0.05A. In theory you could run 20 fans off one header, but I don't really know of an ITX case that uses that many.
One of the spec sheets on the product page shows:
1x DC Jack Colay 6pin ATX
and the next says:
2: PWR_IN (6PIN 12V/19V).
I thought this means that it can be powered internally and externally using either 12V or 19V.
A @ParallaxStax mentioned, you've got a lot more clearance than you think. Unless you plan on doing something custom that limits your cooler height, we would have to know what the max height can be so that we can give you some suggestions. That Prolimatech with a 25mm fan would be around 70mm...