There is no difference between the i7 and i5 for gaming currently EXCEPT if you also run other things in parallel that require processing power. So streaming, recording, video editing, etc. But if you aren't looking to do 10 things at once while you're playing games then I would go for the i5 because there's literally no difference in performance.
What I'd do is read up on overclocking as that will help you quite a bit in the games you play. But don't worry about it too much, you don't have to do it right now, you can do it a year later or whenever but keep it in mind,
The first build stulid posted for 872 is pretty good though I'd go for a different case (Phanteks Enthoo Pro). As for monitors, I've recently got my hands on an Iiyama XB2783HSU and I can say it's absolutely gorgeous for 1080p gaming, have a look at it. I like basic mice/keyboards, so I go for whatever keyboard I can find and for mouse a Logitech M100 is excellent, fits just right into my hand and works well. I've been using the same type for basically 10 years now.