I'm not sure you can get the electrical done as cheap as you think. The issue is where the transfer switch is installed vs. where the generator is installed.
Around here. You have to notify the electric company you are installing a generator and transfer switch. They want the make and model and which electrician will be doing the install. They have to send out someone to pull the meter during the transfer switch installation.
One other thing, you will need to get Soft Starts for your Air Conditioners. And even with 20kW, you need to be careful on electrical usage. Don't use an electric dryer or an electric oven/stove if the Air Conditioners are running.
https://eltwin-hyper.com/