Algae scrubbers

[spit.fire]

So I've been thinking about adding an algae scrubber to my system as I have boatloads of room under my tank and I'm looking for some advice, I'm planning on running it off of the return on one of the smaller tanks on my system (tank contains 11 engineer gobies and 2 clams)

What angle should my "mat" be on?

Do I have to seed it with hair algae? (I don't have any in that system that I know of)

What kind of flow is recommended?