I love this idea. If in some way the system produced more of the "seeds", and each of those "seeds" resulted in slightly different carbon chains, we could increase the diversity of the food in interesting ways.

And if the system is large enough, and could be made beautiful, one could take a walk through the system. Call it a "forest".

And it would be mad if these "forests" would grow on a planet-sized spaceship with atmosphere and plenty of water, how cool and scifi would be that!

We already have a (kinda magical) device which does that. It's also clean to build, can self-build and self-copy, is edible.

It's called a vegetable.

Most veggies are mostly water by weight/volume so it wouldn't be a good deal. They also have very little actual calories.

What you want is actually cereal. They probably absorb a bit let CO2 than trees but at least you can eat them so that's more useful.