Looks okay, with one worry...

The 300s (like most of the good antecs 8V) have the power supply on the bottom of the case. With this microATX board in a mid tower, the atx power cable for the mobo will have to reach from the power supply at the very bottom of the case, to the mobo jack at the very top middle of the case. The power cable might have to be squeezed around the GPU card.

It's rarely an issue with new hardware, antec tends to be good about cable length (almost a cable management nightmare in some situations) but I would check specs on the PSU cable length, just to make sure it will reach the height of the case, with some slack.

Edit:
Case: 18.30" x 8.10" x 18.00"
Antec ATX Power Length 550mm 21.6" - http://www.antec.com/pdf/flyers/NeoEco520C_flyer.pdf

You should be good 8)