Ir2153

Hi.
I want ti build small half-bridge smps ( offline ) based on IR2153. I saw few schematics here on the forum ( and here, and here ) and have some questions:
- Oscillator frequency for IR2153 is Fosc ~ 1/(1.4xRtxCt). But, what is switching frequency ? Is it equal to Fosc, or is it 1/2Fosc ?
- Do I need small inductor in series with primary of output transformer ? What is the value of this inductor ? It probably depends on primary leakage inductance of transformer, but need to know how to choose proper value. Do I need snubber for it ?
- I never saw somebody using fast diodes in gates of switching transistor ( parallel with gate resistors ) - for faster turn off. Can I add them, or there is some reason because nobody using them ?