Is this a good "pure" sine wave inverter design?
You say you're not familiar with digital oscillators yet, but I think it's worth looking into. Using a microcontroller with PWM output you can input the signal directly in the amplifier's format. So you won't need an A/D conversion at the amplifier's input stage.
The code for the microcontroller is very simple. Basically it's like this: you need a sine lookup table, and a timer interrupt generating your sample clock. This can be 5kHz, for instance, then you get 100 samples per cycle, which is enough for an inverter application; the transformer will work as a low-pass filter. Every 200\$\mu\$s you take the next value from the table and set the PWM register with this value. The output will be pulse-width modulated following the sine pattern.
This means that your class-D amplifier doesn't need the input stage with the triangle wave generator + comparator (this would otherwise be you A/D converter), so it only consists of the driver stage for driving the output MOSFETs.
You get a crystal precision frequency virtually for free.  



PS: a center-aligned PWM signal will give you a cleaner sine approximation, but many microcontrollers only can generate edge-aligned PWM. This Freescale controller is available in an SOIC-8 package and is an example of a microcontroller which can do center-aligned PWM.



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