Not really, it's just a matter of how many resources you have in use vs. available memory. A sprite is either in RAM or it isn't.
Script also changes the game big time. Depending on how they are written, you could be eating up TONS of RAM. Usually this is only a problem on the PSP or DC, since the Wii has quite a bit more RAM than either of them. Still, it's no where near what even the lowest end PC has.
Turn on the Frame Rate display in options and you can see current RAM usage. If it's more than 75% of a consoles given max RAM, your module is probably just going to be too much for it. My own projects (which are on hold bit still in place) were and are every bit as ambitious as yours, and I can tell you there is no way any of them are going to run on the PSP or DC any time soon - probably not the Wii either. It's just a trade off you might have to make for features vs. console compatibility.
I assume you know to #import functions instead of #including them; if not you are throwing at least half of your RAM away. Other than that just try to optimize your scripts as much as possible. Clean out variables and such, don't use what you don't need and so on. You know your way around a script well enough to know what I'm talking about.
Another would be to avoid load. There are tricks to load only what is selected for use and unload it otherwise. It's a PITA to do, but something that might help when you want to include a lot of playable models.
As far as Wii specific issues go, I'm afraid our resident Wii port guy (Plombo) has gone MIA for the time being. We'll see if he stops in and has anything to offer.
DC