Is there anything wrong with my current setup for LED
Is there anything wrong with having the PWM dimmer AFTER the Buck Boost converter? ... Should I move the PWM dimmer BEFORE the Buck/Boost converter?

Neither.  A separate PWM modulator for dimming is pointless duplication, since you already have a switching power supply in there anyway.

You say can you can run the switcher in current controlled mode.  Modulate the light level by changing the current control input to the switcher.

You can think of the switching regulator as a sortof filtered PWM modulator already.  Instead of feeding this regulator pulses, or drawing current from it in pulses, have it make the average current you want in the first place.  This will be more efficient since there won't be yet another pass element in series, and more control logic to power.

Also, drawing current pulses from a constant current supply is a great way to make it unstable.  Don't do that.