I think the Rock work looks fantastic. Too many tanks these days are doing the 'minimal' rock approach, which I think has a nice aesthetic, but is not an environment that more delicate fish do well in.
With your rock structure there is plenty of hiding spots for shyer and smaller fish, and giving them an area to hide and hunt for food will give you a lot more fish opportunities to add to the tank.
If you need help with the Apex (plotting what you need, what components to order, and where to order from), shoot me a PM. I have helped out and installed over 20 Apex and a few of them are extremely complex, with separate buildings for tanks and filtration equipment. So helping you plan for your tank vs sump garage I may have some insight for you.
Dave B