1. Yes sand and dirt works fine
2. No problems with mts
3. It could work, but keep in mind dips are harsh on plants
4. Most of your mts will go away after a substrate switch.
5. No it doesnt need to be rinsed and dried.
6. Just go ahead and build a stand. Make it look nice and see if she gives the okay on it. They arent terribly expensive. Worst case scenario you can sell it.
"The simplest explanation for some phenomenon is more likely to be accurate than more complicated explanations." -Occam's razor