First Gaming Rig

[TouchandFeel]

As Noxifer pointed out, the main difference between MicroATX and ATX is size. Basic performance will be the same, but the space everything is crammed in as well as the number of things like expansion slots will most likely be smaller.

As this is your first build, go with ATX as the extra space will probably make it a bit easier for you to work with.

Most of the main hardware manufacturers make good stuff and the biggest difference in performance/quality will be between models, so find one you may be interested in and read lots of reviews on it, both user and professional.

As for the 8gb vs. 16gb debate, it depends.

If you are pretty much just using this rig to play FF14, then yeah 8gb is enough as long as you don't go crazy with multitasking. If you are going to be doing a lot of multitasking while gaming, then you may want more. Also keep in mind that we are starting to see games come out now that have 8gb under recommended specs , but can push past that fairly easily with just basic multitasking.

The reason I recommended upgrading to 16gb is because its cheap and gives you headroom that you may need, or not. That will depend on your own personal usage.
Me personally, I chew through 8gb easy, but I also run everything at QHD resolution or 4k, run max settings, do a lot of image editing and use a lot of power hungry memory hogs of software.
So is "8gb is enough" gospel like many people like to say? IMO, no. For many people it will be enough, but mileage will vary upon usage.

If the extra $40 is questionable to you, get the 8gb and monitor your memory usage while gaming and how you would normally use your computer. If you start getting close to 8gb of usage, then upgrade to more. Otherwise you can just stick with the 8gb.

However, if you do switch to a 970 instead of the 960 as others recommended (I agree, the 970 are best bang for your buck), then you can probably just stick with the 8gb as the extra 1.5gb+.5gb of dedicated video RAM will be a much bigger performance boost for gaming and will help minimize the need for more system RAM.

One more thing, when you select your CPU Heatsink, check to see if it comes with thermal paste. If not, make sure to get some or else you won't be able to use the heatsink.

Edit: Out of curiosity, why the ssd and separate hdd? Do you plan to install the OS on the ssd and games on the hdd? If so, is Steam your main PC gaming portal (no pun intended)?