As /u/DanielStraight said, it all depends on the requirements for your project.
In the meantime though, I would recommend working out some prototypes, both to brush up your skills and also to get some ideas on the architecture/design. Since you mentioned that this is a desktop app, maybe try out some tools/frameworks that you might end up using in the final project.
MvvmCross = imperative programming, mutable state in your UI & pub/sub messaging based API design.
ReactiveUI = declarative/functional reactive programming, reactive extensions & subscription/observable based API design.
Considering he is a intern/newbie, just getting started and has a deadline of a month I wouldn't suggest these two at all. Both projects have a vibrant community but have not crossed the chasm, samples and documentation needed to onboard absolute newbies is far and few between.
Argh..this is way ahead of me for now...I need to learn about RESTful apis first right ? I never did any networking using WinFomrs or WPF either..Why would I need networking services this in a desktop application? Reservations and all other tasks are done by the hotel staff.
In the meantime though, I would recommend working out some prototypes, both to brush up your skills and also to get some ideas on the architecture/design. Since you mentioned that this is a desktop app, maybe try out some tools/frameworks that you might end up using in the final project.
Here are a few recommendations:
https://github.com/Squirrel/Squirrel.Windows
https://github.com/akavache/Akavache
http://reactiveui.net/
http://mahapps.com/
https://github.com/MvvmCross/MvvmCross