Thank you, bosqueberg and bach!
I'm sharing a garden and a big windowsill with 2 flatmates. There's some basil, chili, strawberries, succulents, calendula and a young apple tree growing here and there, all of them mostly their projects, not mine. I've been more of a mushroom guy for the last years, and enjoy IDing various species (or at least genera) when going on walks. I did care for some tiny oak and beech saplings when I was around 9; I guess that's too long ago to really matter much, though.
To elaborate on the terrarium further, I'm imagining a 40x40x70cm^3 glass room with ~4500K lighting from directly above, humidifier blowing mist down, a two-story interior with light-loving, tiny-leaved vines on top, a 'nursery' area on the bottom and maybe a bioluminescent mushroom growing from a log in the shade. Also a big monstera or philodendron growing beside/above the terrarium.
I'm thinking traditional terrarium plants like ficus pumila and moss might be a good start, just to get some scenery and humidity into the chamber. First priorities are lights and soil composition, though. Photos will follow as soon as I get the right piece of furniture to place it on.
I'm open for any suggestions you might have, too!
Also, I'll add some eyecandy of amanita muscaria and laetiporus sulphureus, because they're both vibrant colours and need plants to thrive.