why would they not have 7th level slots if you rest and then they duplicate you with a 7th level spell slot then the new simmulacri would have 7th level spell slots
I have to disagree with that. I believe feats provide lots of richness and Depth as well as helping achieve character concepts. Also as a Min/Maxer I can tell you that almost all of the abilities in the player's handbook are written with Multiclassing in mind.
the thing that I think bothers me about the first two aproaches is they are just dm saying "no!" rather obviously but the third option seems more like an actual story tied limit to simulacrum that would be less likely to make players feel like dm was just outright saying "no!"
well they copy the statistics of the creature that is targeted so if you take a rest to regain those slots before they copied you then they would have a 7th level slot
no the spell says if you cast the spell again previous simulacrums are destroyed and the simulacrums can work as completely independent cretures so every clone could only create one more clone