I have always bought new tanks for when I move. WHen I move here from my apartment, I'll be moving my 75g, 30g, and 29g and they'll be moved into an already cycled 240g. I moved my 30g that was at home and it was put into a 75g that was cycled here then moved the 30g empty to start over. As far as the rock and sand, I did as was suggested above, sorta. I trashed most of the sand. As I will do with what I have now. I'll kep a big bag full of sand that's in water to help bring in the good bacteria and the rock will be in rubbermaid tubs with as much water in it as I can with soaked towels over them. I think the best thing you can do is what you're doing now, establishing a plan ahead of time.
This thread is making me dread moving all my stuff, not just my tanks in a couple months.