Is this a good pre built pc for gaming?

So I was planning on making my own pc build, but everything added up to 1,050 dollars including the monitor, so then I saw this PC that was on sale at microcenter, here is the link:

http://www.microcenter.com/product/439980/ProDesk_...

Please look at the specs, and tell me if it's a good deal cause Im really curious, my pc build was similar to this one.

So I will replace the gpu with a GTX 960 and switch the psu to a 600w, monitor (1920 x 1080p) will cost like 150, so the cost will be around 875 dollars.

My questions are: Will this pc run all current games and MMO's on ultra at 60+ frames?

Do you think the GTX 960 will fit in the case?

Can I use a xbox 360 controller for it?

Oh, and the woman said at Microcenter that I should have them take out the gpu and have them put in the GTX 960 and psu, because there's alot of security protocals you need to do like deleting files, restarting computer, blah blah blah, is that true? (Will cost me 80 bucks)

Btw there's no other memory slots available.

And PCI slots are limited (I think)

(Not a great motherboard)

(3.2 Ghz)

For some reason they say its a business pc but whatever.

And im not a fan of windows 8.1 so that's why Im also being cautious,

SO please tell me if this will be a great PC to buy for gaming.

If you have any advice for me, or suggestions or changes with the gpu or anything else, please tell me. I really need help cause its on sale for like another 3 days, thank you.