I think a movie would be a big ask.
There's so many different settings in the book such as the keep at Crydee, the elven forest, stone mountain, the swamps on kelewan, the magican city where Pug becomes a great one(forgot it's name). for a studio to set up all these different sets would cost a fortune so they would probably end up cutting huge chunks from the book and that would spoil the story IMO.
Theres nothing worse than having read the book, large and important parts of the story don't make it into the film.
As an example i read V.M.M's The last Legion and enjoyed it, the film totally sucked with the whole middle part of the story not in the film.
I suppose that two films might work, but i've only read magican as one book so don't really know where the break off point is.
With regards to a mini series, I wouldn't like to see magican as a MS. It would take years to complete and therefore theres a chance that whoever started it could cut the series and you end up getting a couple of seasons without the end.
Perhaps a book like Honoured Enemy would make a good mini-series, seems like it would be a easy story to transfer into a tv show?