Dirt becomes messy when pulling up plants. The roots will pull up dirt particles. If you aren't planning to use a bunch of stems that requiring topping and removing the older growth you won't have much of a mess./QUOTE]
Stemmed plants are not a problem in dirt. You can either let new bushy growth come up from the stems, or you can cut the stems off at the base, leaving the roots in the dirt and replanting the tops.
Yes, it will. 1.5" is max. 1" is more common.2 inches of sand? Will that be to much?
A deeper cap gives you more room for error, but can also lead to anaerobic bacteria growth. You have a massive tank, so anaerobic bacteria is not as big a concern. Just poke the substrate with a chopstick every few months.
A deeper cap will also make it much harder to grow carpeting plants, which may be unable to reach through your cap to the soil below.
As MtAnimals mentioned, the most important step in preventing dirt mess is to avoid cap breach while you fill your tank. I like to place plastic wrap and filter sponge over the substrate and pour over that to disperse the flow.
