High Voltage Half Bridge Drive
You don't show the whole circuit, so it is impossible to give a precise answer.

Your upper PWM signal will need to be isolated from the lower one with a circuit that rejects up to 1000 V of common-mode signal at 50 kHz. An optocoupler might work, but you also have to provide power to it on the output side.

When you power this circuit up, the generated signals at the transformer may depend on the EXACT duty signal. Without feedback, you will be unable to regulate at 50 % overall, and the junction of C1,C2 will charge to the supply rail or GND, thus making the drive asymmetrical and unable to provide good PWM signals.

C3 cannot be charged to over the (peak-rectified) mains in this circuit. It will basically be a constant DC voltage unless the load power is significant w.r.t the lamp power.

It's high voltage and potentially lethal. If you do't know the basics, then you are working with very dangerous voltages and energy storage.