You might also consider using constant current LED drivers. There are many on the market these days and many (most?) of them can be controlled with PWM signals. I suspect that as you develop your design, your LED driver circuitry will evolve into something that's more expensive than just using an off-the-shelf constant current LED driver.
I've used LuxDrive's BuckPucks
to drive high power LEDs in a couple of my projects (Crystal Ball Lamp
and my chandelier
). However, they're kind of pricy and I'm guessing there are less expensive alternatives available these days.
Hope that helps and have fun with your project!