How much will you get per month by mining with a 1080?

not too much, 100-500$

Maybe you should use this calculator (few Graphic cards more canbe checked out):

https://www.nicehash.com/?p=calc

PS: An ASIC miner is always better for mining.

How much can be made from mining from a Mac computer?

A single 1080 won't get you much.
You're better off day-trading.