Sure, Aqua Soil could go a ways in helping you to grow some plants, even in a low-tech setting. But it is in no way necessary. Honestly, if you plan on growing relatively easy and low light plants, it's just a waste. And it would be crazy expensive in such a large tank.
Anubias and Java Fern gain nothing from it, since they aren't even rooted in the substrate. Beyond that, and depending on how densely you plan on planting the tank, my advice is to go with an inert substrate and use root tabs under the heavy root feeders like swords.
You have plenty of options, though, depending on how much you're willing to spend and do. If you're completely tearing up the tank and the substrate anyway, mineralized top soil works amazingly, and is basically free from your backyard. Lay some of that down and cap it with a couple inches of whatever you like and you're set for next to nothing. Or you can go with something like Turface, which is a fired clay product similar to Flourite, just a lot cheaper and not marketed towards aquaria. I'd still use root tabs under the heavy heavy root feeders with it though. And then you could go completely inert, with just a few root tabs where you feel like you need them, and you would still be fine, in all likelihood.
If you're keeping it low tech and low light, save some money.
And welcome to TPT!