I like your idea to access the back of the components for routing cables and easy connections to dedicated power. What a convenient place for a storage/electrical utility room. Consider routing your cable/internet into that room too so you can easily hard wire network cables.
I would rough out a design and enlist a carpenter to make the front look however you and your SO want it to look - a door with leaded glass panes could be cool, but a solid door or no door could work too. I would consider built-in vertically adjustable shelves, not a slide in rack. If you really want a slide in rack, look at Sound Anchors. They will make whatever size you want and you can put it on castors or sliders (like Herbie's Giant Threaded Stud Gliders). Consider ventilation - a passive approach would be best but if you have a lot of tubes a fan may be necessary.
For shelves figure out how to provide very solid supports connected directly to the wall studs (consider 6-inch doubled-up studs on the sides). Preferrably the supports can have with some adjustability for changing the opening heights between shelves. You can then select the shelf material and design of your choosing. I would probably look at thick wood planks for simplicity and esthetics. If you want to get fancy, have some steel frames welded that can be connected to height-adjustable supports on the sides. Powder coat the steel and select some nice looking wood to sit on the steel shelf frames.
Some very good audio racks use elastomeric material to support the shelves (like this one), which would be easy to incorporate into the shelf supports using commonly available elastomeric materials like these or these, or Herbie’s products.
Finally, consider where your speakers are going to go and allow a method for routing speaker cables. If you use monoblock amplifiers sitting next to the speakers, consider how you are going to power those. Also, consider power and cables for subs, both at the front wall and at the rear wall in case you later decide to go with a four sub (swarm-type) set-up.
Have fun!