VGA design from 0-5GHz bandwidth

I'm designing a project with 0-5GHz VGA. With 1dB gain steps from 12dB to 20dB. Power less than 1W. 50 Ohm input/output impedance.

My architecture is using resistive CS amplifiers (2 stage cascaded), then use the attenuator with variable transistor widths to vary the gain.

1. Is my architecture correct ? 

2. I'm getting very high output impedance ~700-800 ohm. How do I bring it to 50 Ohm ?

3. Can I use common-drain at output stage as a buffer ?

Thanks 

Param