even if you stick to 1 strain, there can be great variation from one to the other, which can make evening out and applying light effectively to all plants difficult. Less so with photoperiods, but more of a crapshoot with autos even if you stick to 1 strain.
There are ways to train them to level out the canopy. Easy to do even if your first time, but the timing and where to bend or this or that does take some familiarity... good thing to learn. Learn by doing.
can bend or break stems, tie them down... etc etc.. try to keep height as even as possible.
"souvenir" is a poor attempt to avoid legality issues, lol. Like those waiver forms you sign before entering or doing something dangerous, it won't hold up in court. Check your local laws. May not be relevant for you. In the US, for example, the person who posts the seeds has risk, but the receiver is not legally responsible for what was sent to them. Otherwise, you could just get your enemies thrown in jail by sending them illegal things.