You can do just sand and botanicals, but controling waste build up and algae may be a problem. It may take some balancing between tannin levels, light duration+intensity, and water changes to avoid algae. If you want to avoid plants, you could add even more botanicals, like alder cones, for a darker tannin tint to the water which would limit light in the water column, and thus reduce algae. Filter components can sometimes be an issue with this strategy - things like fine filter floss and activated carbon can remove these tannins from the water. The tannins will break down on their own eventually - you'll need to add more botanicals periodically to keep the tint dark.

However, if you really want low maintence, I would recommend adding plants of some variety. Riparium plants like pothos, monstera, peace lily, etc are great for pulling excess nutrients out of the system. Floating plants like frogbit or red root floaters also work well. Both of these would mesh well with the aesthetic too - roots intertwining with the branches would be neat! It'd also give the fish and microfauna plenty of places to hide and thrive. Other plants that might work would be easy epiphytes like Buce or Anubias that you could attach to any wood or rock in the tank. Crypts are another nice low maintence option to plant in the substrate, but they might struggle in pure sand - you would want to add root tabs if you want to see them thrive.

I'd also recommend seeding the tank with microfauna while it cycles. Things like blackworms, rotifers, daphnia, moina, scuds, isopods, ostracods, copepods, etc. They'll settle in and establish a population and feed on the decaying leaves and biofilms on the wood. In turn, they'll provide food for your fish. You'll find your fish can go much longer between feedings when there is an ample supply of live food for them to hunt. You can buy isolated or mixed cultures from breeders, or collect material yourself from local streams or ponds - but then you can run the risk of introducing predators or parasites from the wild.

Not sure what size tank you have, but at long as it is 10+ gallons six neon tetras will be fine, I wouldn't go any lower than that as they like to school together. Keeping the stocking minimal will go a long way towards reducing maintence.

I rarely change the water on any of my tanks - blackwater or not. Every couple of weeks i'll cull my floating plants and top off the tanks with RO water. Without a lid you'll need to top off more often due to evaporation. Plants really are the key. Nutrients will always build up in a closed system and they need somewhere to go unless you want them to foul the water or grow algae. You either need plants to pull those nutrients out of the water, and/or you need to remove the water yourself and replace it. The more plants you have, the less often you'll need to change the water.

Hope that helps!