I don’t think there’s any harm in recreating an environment as a homage to the original, I doubt you’d run into issues. If Eidos did complain you can just change names and any copyrighted material without compromising the project. A dark, low-fantasy stealth game set in a quasi-medieval period is not a registered trademark 
What I would say is that you should look to do your own learning first and start the project yourself. As someone with no skills or experience, you will find it hard to attract and motivate a team of people to help. The question in everyone’s mind would be “we’ve all played Thief and know what it’s about, why do we need you?”.
I think you should start working solo and build up the skills so that you can make a real, tangible contribution to your own project. Volunteer projects like these also have a very high turnover of people, so you need to be able to keep the project going when one or more team members leave due to real life reasons.