Definitely use a single substrate (no capping). If you use root tabs, you'll probably end up with a lot of little fert balls hanging around from frequent rescaping. I would probably go with one of the baked clay (or volcanic clay) variants (Flourite, Eco Complete, Turface, Diamond Pro, the AP brand, etc.) because of the high CEC, knowing that they'd absorb nutrients from the water column and mulm that settles on them, and when you rescaped and mixed the substrate up, you'd end up with nutrients further down in the substrate ...sort of like root tabs.
I'm very tempted by ADA New Amazonia or II because of its nutrients (not a fan of having to dose all the time) and being able to hold a slope well because I'd be doing a mountainscape at some point, but I've heard it breaks down easily, especially with frequent rescape. Just wondering ADA would be fine for me and if the mud-like AS later on would be fine for continuous use as well?
I don't see how the little fert balls would be a problem during rescape since I can buy a mesh or something and filter them out. Or not, and they can be mixed and just use the PFS again?
I wouldn't crush up the root tabs - would likely make quite a mess of/in the sand. Put them in whole, and if your sand is say 3" deep where your plantings are, push them right down to the bottom, and you should have no problem messing up or coloring up the sand when you do your re-scaping.
And no, the fert nutrients in the tabs would not float in the water. PFS sand is quite dense and will properly hold in the tabs until they disappear from being drawn up by the plants.
I'm a complete newbie to this: would carpet plants do well on PFS? Would I also need something under to help the sand hold its shape? ie gentle slope.
I'm tossing up between ADA and PFS. With ADA, the nutrients, probably easier to source and slope holding. With PFS, for the price, ease of rescape, and I will be using PFS for my main tank when I get to it.