Juliet, your "weird" Scenario is interesting.
Some disjointed thoughts that crossed my mind as I read it:
Could be a clone rather than a hired impersonator. Each idea leads in a different direction.
The hired impersonator gives a great op for a completely out of character Clark (rather than just a childish one that we might get with a clone) The impersonator could lead to all sorts of fun for Lois as she notices that Clark is "not quite himself" and tries to make sense of it. I see a great B & E opportunity for her
(among other possibilities)
Lex, who's trying to woo Lois and destroy the Planet
Umm, I don't see Lex trying to woo Lois as there's no Superman around - I never thought Lex was interested in Lois per se, but in her 'trophy' quality in his competition with Superman. But I can see him trying to bed her - in S1 he's very much the womanizer. But all that introduces an interesting complication - has Lois found out something damning about Lex???
he could have people combing through Clark's past and/or he could have obtained Trask's file on him from Bearu 31 and deemed him a nutcase while still valuing the info on Clark's life in the file
A plot challenge here - why would Lex's people come across Trask's files in the natural process of what they're doing? But I'm sure this could be worked out.
Your idea of exploring the reactions of Lois, and M & J to Imposter Clark (Bizarro?) is interesting - a story in sections, maybe: Lois's POV. then next chapt. J's etc?
Bet others have all sorts of ideas for your story, Juliet. You should give it a shot.
c.