If you have a 120g limit, 3 sq ft can do that.. less than half of that tent. Might need a 100-150w light depending on the efficacy of it. Maybe 4 plants in a mini sea of green that you do 12/12 for 7-14 days. A 5L is quite small, so you'd want to fill with as many tiny plants as it takes.
if the light has a rectangular footprint due to shape, maybe 2 rows of 3 plants. Leaves lots of room for a circulation fan or exhaust fant to fit into tent if not using the full 0.64m^2 space. With more plants probably wouldn't need any vege time at all, and just 12/12 from seed.
Trial and error with that stuff.
With a 20L, 1 plant might be enough with 4-5 weeks of vege if you get a decent growth rate from seed.
Just with basic plant maintenance and filling an intended size of grow area you should be able to do 50grams/sq ft.
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