I like your 75g. Personally I like alot more hardscape, driftwood, rocks, etc. That being said I'm not as good at planting as you are, so I need the hardscape for transitions. Your plans for your other tanks would definately be awesome and something I would follow. My wife is at her limit withthe tanks, the space they take up and the time I spend on them. Unfortunately a rack isn't feasable as I have a 75g, a 46g bow, and a 29g in addition to my 10g and 20g. I had to put the 10 in my closet!! Luckily I have a big closet.
Congrats on the engagement. My first marriage tore me up and I had to see a therapist and take quite a long period of time off of work. I swore I would never become attached to a woman again much less get married. My wife (we were married on May 13) spent 3 years patiently changing my mind. I know I did it right this time. It's amazing what the right woman can do for you! Good luck on the RAOK.