Unless it is closely related to your core business you should exercise influence to point out that this is poor judgement on your boss's part.

If you have all the funds needed for the project, you could start to

- write a project outline

- put a core team together

- refine the project outline

- take it from there... step by step

If you're the manager, you'll have to rely on other people for the technical knowledge. The question is not "How To Build A Turbine Generator?" It is "How to get the project going?"

There are a lot of companies who will sell you a new or rebuilt gas turbine of any size you could possibly want, so that isn't particularly new or interesting. There is a growing interest in developing small turbines for distributed power production. These may look more like a turbocharger than an aircraft engine. Turbochargers aren't cheap, but aircraft engines are shockingly expensive. Some advances have been made with ceramics and not so much with 3D printing (of the electric arc type). Current efficiencies aren't good, but there's hope. If you could make little turbines that weren't too expensive and didn't consume too much fuel, people would buy them to get off the grid. Right now natural gas is really cheap and available in many neighborhoods. The price will go up eventually, but there are other fuels. You aren't limited to a once-through system. People are now working with various regenerative designs to increase the efficiency and reduce waste heat. This is an area where new innovative ideas could make a big difference, especially if you got an international patent! It may sound like a crazy idea, but so did that silly thing the Wright brothers took to Kitty Hawk.

What I need help with is the design steps

what to calculate, then what to calculate next

First of all, you should clarify with your boss some details of the projects: purpose, rated power, fuel, location, etc, in order to focus your research.

Secondly, you have to calculate the Brayton thermal cycle. After that you should design the machines and equipments: gas turbine, compressor, combustion chamber, control system.

Finally, you will find builders for all of that and an installer for the whole.

It's cheaper and easier to buy the final product instead to do-it-yourself.