(there was one I read and I can't remember offhand which fic it was, but it had Nephrite trying to boost Akane's passion for cooking to drain her energy and it horrifically backfired on him after he was forced to eat it)
I think i have read that...
Has some variant of this idea been done?
Only partially.
Nodoka taking 'Ranko Tendo' over to a jewelry sale at OSA-P
Kuno visiting a certain fortune teller in Azabu to get advice on how to free his pig-tailed goddess from the clutches of the vile sorcerer Ranma Saotome
Kasumi having her pure heart crystal being targeted by one of the Witches 5Those 3 i have seen in one fic, and that´s about the most of it.
Timeline-wise I'm not sure if it's better for this to run somewhat concurrent to the Ranma timeline, or if it'd be better to have it all be after the failed wedding.
SM stretches out a fair bit in time so you could start during the Ranma timeline if you want any changes made to it.
I had an idea for a fic where the events of the Sailor Moon anime are happening in the background, and we're seeing the effects of what happens in Sailor Moon reach the NWC.
Just make sure you have a story of some kind, either for the crossover combination, or for the series you use as primary, so you avoid just parroting original events from both series, as that generally only works well as parody.
Of course, letting the story be whatever changes the crossover interaction causes works as "the story" as well.