Have you considered being a taxi driver?
Depends on what city you live in but it ticks most of the boxes you require.
The main one being flexibility in working hours, you can choose when and how long you wish to work for. This in turn will determine how much money you make from it.
You will pay a monthly/weekly fee to the depot and licensing costs and seeing as your air crew already you should have no problem passing the medical.
Whatever second job you take on remember you will have to declare the earings to the tax man and also check your pilot contract as it may state you can not work a second job.
Good Luck!
Aka.