1) a lot. I personally have one with an LSI 9280-8e, and another with an Areca ARC-1882X (with optional management port daughterboard removed to make it half height).
2) You can definitely break off the perforated section on that board to make it shorter... I didn't check the dimensions.
Something to keep in mind is that you can get extra space for the pcie card by removing the front antenna bracket, it gives you a significant amount of space:
View attachment 35528
Single screw where the arrow is to remove it, other end is just hooked in.
If you happen to be using wifi and have an antenna there, you can detach it from the bracket and kind of "wedge" it in between the cpu cooler fan and the pcie card (up at the top of the highlighted bracket part in the picture)... little bit of VHB tape to hold it if needed.