I assume you don't want to follow the ideas shown in the end of the movie? But some of those may have followed in the book as well.Annie could have continued in PR, she was doing a great job of turning a near disaster into a triumph for NASA.
Beck and Johanssen stay with NASA, and become a couple. Vogal goes back to Germany, maybe works for ESA. Martinez resigns from NASA and becomes a pilot for SpaceX, returning to Mars on one of their colony ships in 10 years time. Your idea for Lewis works for me as well. Watney trains crews in survival techniques, and eventually finds out how to grow crops in Martian soil without using poop.
Mitch resigns from NASA and works in private space.
Teddy remains as administrator or directer, whatever he is, for a few more years before he retires.
Rich keeps working on trajectories, and finds a few ways to save a couple of days on flight times to Mars and back. He finds ways to get the supply missions there faster, so the flights can actually speed up.
Venkat remains as the head of the Ares program, and brings more international cooperation into the program. Soon, Chinese and Russians will join the American, European and Japanese crew members who have already flown to Mars.
I doubt Ares IV would fly as scheduled. It would need a new MAV at least. Ares V and eventually Ares VI gets approved and flies as well.
The Hermes flies all six of these missions before she is retired, and a new ship is built. Hermes is placed in Earth orbit and becomes a destination for tourists flying on SpaceShipFour and the Dragon Cruisers.