Avid's not pushing anyone to go subscription, you can still buy perpetual licenses for their products. They're simply offering another option for those that find it financially beneficial. And for the price of SF, you could get the industry standard for not much more.
Another good DAW option is Reaper, you can skin it however you want (I like the Pro Tools theme), costs just $60 to remove the nag screen (but is still fully functional with the nag) and there's a cheap plugin that will allow you to import an AAF from your NLE.
Personally, I think Logic would be a better DAW than SF (I used to use SF on Windows) for film work.
The annual upgrade plan simply means you pay the $599 and you can use it as long as you want. Forever. If you decide to upgrade, it's only $99 at that point, but they won't make you upgrade.
Logic isn't just for music, no. It's great for mixing and cleanup as well. I personally don't use it, but have friends that do and they love it.
You can purchase iZoetrope for any software you plan to use. Currently, I bounce between Pro Tools and Reaper for everything - music, mixing and cleanup. Both programs are perfectly capable and do the job, it really just depends on my mood or the project.