Side panels are switchable. I just did a build with this case a few weeks ago (my first build ever) and it was surprisingly easy.
Few things that may help your build:
1) HD Audio cable is a bit too short to run through the cable passthroughs to your HD Audio Header if you have a ATX mobo (mATX should not be an issue). I used this extension:
http://www.performance-pcs.com/cata...ge=product_info&cPath=34_83&products_id=27433
2) It does not come with rubber grommets for the cable passthroughs. They are not necessary, but clean up the look nicely. I used the large grommets from a 600T/650D/800D fit perfectly and if I remember correctly I used 4 of them. I used these (came with the most grommets for the same price):
http://www.performance-pcs.com/cata...product_info&cPath=130_1012&products_id=31929
Corsair also sells the grommets, but they are $1 more. I still have, bunch of the larger grommets so if you PM we can work something out via paypal and I can save you a few $ if you are so inclined.
3) I have not purchased it yet but the side panel is available directly from Corsiar:
http://www.corsair.com/us/300r-right-side-panel-plain-black.html
4) The right panel (mobo cutout side) is a bit of a tight fit due to the thickness of the CPU and ATX backup power cables (my PS is a Corsair AX650 which is sleeved and modular). So plan accordingly, I did not really realize this when I started (again my first build). But, I did take a lot of time planning/sorting out the cable managment so it was not an issue for me.
5) If mounting an SSD you just need to remove one of the back pins (just pop/push it out with a screwdriver) and screw the SSD in with the provided small screws. The rest of the drivebays are toolless for nonSSD parts.
6) If you are using 2 140MM fans on the top of the case, the front one (closed to the drivebays) will block the top 5.25" bay. A 120MM should not. I just added 2 extra Courgar 140MM fans one on the top back as exhaust and one in the front under the stock one as intake and temps are great.
It is a great case, hope that helps.