Help...Want to start from scratch....


I have been running a 75gal for 3 years now and we are in the process of finishing our basement. Almost finished with the wiring and framing and just decided that it might be a good idea to do an "In the wall" set up with access to the tank in the unfinished portion of the basement.
I am looking for some good ideas to start this thing from scratch....thinking of maybe going a little bigger and adding a refugium, water top off from my R/O, etc...since I will have easy access to the back of the aquarium as only the front panel will be in full view of the finished basement. Any ideas or help before I begin this project?
Current setup:
75 gal (Yellow tang, clow, watchman goby, cleaner shrimp, snails and crabs)
20 gal sump
220 Watt PC Lighting
Overflow box
Desired set-up:
90 gal?
Top-off system?
PVC Pipe overflow?
Metal Halide?
This shouldn't be too expensive as I won't need a fancy stand, hood, etc.....because most will be hidden behind the scenes.
Any input would be greatly appreciated!