What do you mean by 'proper operation'? The only prerequisites that your circuit has to fulfill is that all your transistor have to be in saturation.

Then, the different biasing voltages are improving some performance parameters and worstening some others. It's always a trade-off between different performance parameters and depends on the specs you want to achieve and your application.

For RF cascode power amplifier, you can varies biasing voltage around 0.2-0.8 V, depend on PDK that you use.

The question is too vague. What technology are you using, what is the amplifier type. There are too many missing details to give a proper answer.

Usually refer to documentation on Vtlin and Idsat information inside PDK reflect to type of transistor that you use.