I am in a similar spot looking at all this..
Can someone who is running a S9 let me know at current difficulty rates, pool fees, how much BTC is one unit (13.5 T/HS) is ACTUALLY generating for you now, per day or per month.
I have some units on the way, I will get them up and running next week, and I will let you know how much I actually generate.
I can tell you 4.7 TH/s is earning about $12 - 14 per day. If you can get 13 TH/s out of S9 figure about $33 - 40 per day.