I made the whole thing (by rough draft #3) in under 3 1/2 hours (Think Braveheart length). As far as actors, I would like to go mostly with unknowns, so it doesn't screw with the thought processes of the audience when trying to 'take in' the whole story. And, of course, all the extras would be filled in with the Myth community. :)
As far as making a movie goes, yes, you would have to have permission from T2. Usually, you "option" the rights. What that means, is you can pay such and such an amount to T2 to make a film in a certain amount of time. There is no contract to actually "make" a film. If you don't do it by the time limit, then you have the right to option again. Usually a contract is set up so that the current option holder has the first dibs on the new option. This basically makes money for the owner on the rights, then, they also make moola off of the finished product.
I can't think of it off the top of my head right now, but some producer optioned the rights for some book, and kept renewing it (he still has a current option) in order for it NOT to be made. Something about how he felt the screen wouldn't do it justice, or something.
There are also different types of options. Some are just to make a film, or TV show. Some include toys and products. Some include both. There are also different time periods.
Aside from an option, T2 themselves could decide to produce (usually not recommended) and hire their own staff, etc... Some book publishers have done this with disastrous results.
My overall plan (and yes, feel free to mock me), is to buy Myth outright from T2, and then make the films. That way, I have the power to do what I wished (don't worry, I'm a purist).
How do I plan to do this? Hopefully my plans will all work out. First, I need to make my first independent feature; the funding for which I just secured and will have within the next two years (sooner, if I can get other funding). After that, upward and onward if it's a hit. Eventual goal? to buy Myth.
It may sound like a pipe dream, but it's mine. I have an actual plan. Now I just need audiences to come see my stuff.
We'll see. Here's to hoping.