BcuzZ's DIY E27 Dutch Passion Auto Grow (1xAuto Orange Bud, 2x Forbidden Cherry, 3x Blueberry)

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.

Does this limit in Germany affect extracts from the plants? I would make everything into hash and maximize my total yield allowed. 120g of hash is better then 120g of bud. Fabric pots are ok, They will dry out faster and make RH a tiny bit higher. Harder to clean and reuse vs plastic. Good Luck!