It would generally be better to put them in pair-wise marriages, but when there's a kaiju on the loose, you can't wait multiple hours to cast it multiple times.
I think an awesome way to use them would be to have the BBEG be a planeswalker. When the fight starts, the DM pulls out a Magic deck and starts playing Magic against D&D.
But you only gave them your name. You never submitted to control.
There's often stuff in fantasy about knowing a being's true name giving you power over them, so you wouldn't want to tell it to a fey. But if they literally took your name, then that would make it theirs, and now you know their true name. Also, according to the forgotten realms wiki, most people don't know their own true name. It's not the same as the name you go by.
Barely. You can throw a potato to get rid of an orc. But this is only occasionally useful and only in the early game. Once it starts costing two or more potatoes to get rid of one orc, it's a bad idea.
I'm assuming that even though the DM pretends to be annoyed, he actually thinks all these shenanigans are awesome and is bending the rules to let them work.
Clone always struck me as something that shouldn't be a spell but is.