To address some of your points, in order:
1. I would frame an extra 1.75" wider than the rack itself for the rough opening in all directions. Use pre-primed 3/4" x 3.5" stock in all dimensions, thereby creating a frame whose interior is just slightly larger than the rack in all dimensions. Slip this casing into the rough opening, shim where needed to preserve square and attach with finish nails. Paint as desired (probably flat black). Build your platform base high enough so when the rack is properly trimmed out as you propose, you can run case molding all around the rack while still having a full run of base molding and a small gap between the two moldings. In other words, if your base is 5" plus a 1" inch gap plus a 3" case molding, and a 1/8" reveal....your base will be 9 1/8" high. The height of your base should be exactly even with the height of the bottom casing. The rack will partially rest on the finish casing and primarily rest on the plywood base. This 3/4" casing all around allows you to create a perfectly square finished dimension inside the rough carpentry and give you a nice edge to attach your case molding all around, just like any window or door casing. It's a very clean look.
2. I personally like rack ears whenever possible - it maximizes ventilation around the equipment, gives a perfect look and often saves both money and rack space. Typically speaking, if you have a piece of equipment that is exactly 3U tall, the RSH shelf will be 4U to accommodate the feet and a bit of space above. When you start adding up all the different pieces of equipment, you can lose quite a number of rack spaces when everything is said and done.
Be careful about the gaming systems in the steel racks from a remote location....this sometimes causes transmission problems between the gaming unit and the controller. Plus, you have to extend all of the USB devices (Kinect, Wii, etc.) to the front of the room to be usable. The good transmitters put the signal over Cat-6, but make sure you weed out any compatibility issues with the USB extenders and these gaming systems FIRST. There are plenty of websites that review this kind of information.
3. Blanks are always popping up on eBay for cheap. Wait to find a guy that has a number of different sizes for a reasonable price and then pop on them. Perhaps this goes without saying....but you don't want to use all blanks...you have to find certain spots for vent panels as well to draw conditioned air past the top of the heat-emitting equipment.
4. You don't need the offset bars, especially with that rack depth. Two 10-packs of standard lacing bars will do just fine....although I prefer the "L" shaped cable lacing bars for equipment that has a ton of wires going to it, like a Preamp, matrix switch, etc. It's just easier to control.
A few other comments:
- It's no problem hard-wiring the power strip provided you get the appropriate metal face plate that allows you to install a Romex strain relief clamp.
- The sliding rack rails are useless to you. Remove them. If you are looking for slide-out storage, just get a Middle Atlantic D3 drawer and be done with it.
- With your system you will not need the Panduit wire management device.
- You can retrofit that shelf that came with the rack with an RSH faceplate. There are ways to buy the faceplate ONLY to save money. Same is true for the deeper rack shelves if you go that route and have the same tabs toward the front that are designed to hold the custom faceplate, fyi.
I hope this helps!