I have two separate tanks I might use, a 29 gallon or a 20 gallon
ok, that's a great tank size!
I would recommend you use the 29 gallons since more water volume means more stable parameters and as such fewer problems if something happens and you cant take proper care of the tank for a few weeks.
A dirted tank would offer the best results since you would not need to fertilize for many years, it would naturally release tannins and lower the ph and encourage a diversity of microorganisms who will have no trouble serving as food for your fish in case you forget to feed them. Also, it would be cheaper than using aquarium plant substrate since you only need a bottom layer of black dirt and on top of that a layer of your favorite natural sand.
A normal 80-watt white lightbar should do just fine and a good old hang on the back filter with its heater, a low tech so it is easier on yourself. for your filer media don't use what they usually come with, rather change that for some coarse sponge and a porous media like lava rock or ceramic media, this will make your filtration more effective, also add a prefilter sponge for your intake to help avoid issues with the small organisms that will be the base of your food chain getting sucked up the filter.
hardscape can be anything you want but I would recommend at least a few pieces of wood and a large rock to help grow biofilm (a really important source of food) and some leaf litter to help sustain micro invertebrates and make detritus (more food sources)
As for plants, I would recommend using front, middle, back, epiphytes, and floating ones of multiple low-tech species, since the more species there is the more diversity, and as such productivity will hold your environment (just like in rain forests).
For front plants, you can use Sagittaria subulata, lialleopsis brasiliensis, and blyxa japonica
For middle plants, you can use cryptocoryne wenditii, and bacopa madagascariensis (I would recommend you leave the middle mainly for hardscape
For background plants, you can use egeria densa, guppy grass, amazon sword, Cabomba caroliniana, rotala rotundifolia, red tiger lotus, hygrophila, hydrilla, Vallisneria, nymphoides Taiwan, and limnophila.
For epiphyte plants, you can use anubias nana, anubias barteri, java fern, and java moss (these plants go glued with superglue in the hardscape, the super glue becomes inert when it comes in contact with water)
Last but not least, for floating plants, you could use Salvinia auriculata, Salvinia nattans, frogbit, and dwarf water lettuce.
Don't be afraid to plant a lot of plant species, since the tank is dirted then they will have no problem finding nutrients and since you are using multiple species instead of just a few, they will sort themselves out and everyone will not have to compete with each other since they all have their own methods (if you used very few species then as they have the same methods of nutrient collection and same nutritional needs then they would have a problem), and, the more plants you have the bigger the bioload your aquarium will be able to handle meaning less maintenance and also a bigger diversity of microorganisms as food for your fish, these microorganisms will come by themselves so don't worry too much.
Now for the fun part, animals, considering that this would be quite an acidic aquarium thanks to the dirt, wood, leaf litter, and plants then I have some stocking ideas that would work perfectly since they have hardy, acidic water fish capable of foraging by themselves, but I will organize it in the centerpiece, a shoal, the cleanup crew so that you can mix and match as you see fit
centerpiece: x1 blue gourami, x2 dwarf gourami, x2 Apistogramma cacatuoides, x2 ramirezi, x1 pearl gourami, x1 paradise fish
shoal: x8 cardinal tetras, x8 porkchop rasboras, x8 harlequin rasboras, x8 rummy nose tetras, x10 neon tetras, x10 ember tetras, x10 chili rasboras
cleanup crew: (a colony of neocaridina shrimp +) x5 golden otocinclus, x5 paleatus corydoras, x5 kuhli loaches, x5 bronze corydoras, x2 farlowella plecos.
now, you should choose no more than 1 centerpiece fish, but you could choose 2 shoals and 2 cleanup crews but that would mean that you would have to feed a bit more and that they would have a harder time finding food by themselves if you fall in an episode and can't feed them for a while, you will also see that I always recommend the neocaridina shrimp as part of the crew, this is because they are the Walstad inhabitants by excellence and because they pretty much don't need to be fed and if in case of you not feeding the aquarium because of a depressive episode their babies nd juveniles would serve as emergency food for the centerpiece and some shoal members.
hope this helps, if anything wasn't clear just tell me so I can explain myself better.
