What would be the best order to read the 4 major works of von Mises?
Depends on your interests.
Economics? Read Human Action.
Epistemology? Read Theory and History.
Monetary Theory? Read TMC.
Socialism? You get the point.
There is no best order to reading the books. They are all self-contained and do not require the others for understanding. If you feel like you are prepared for it, start with Human Action, as it goes over stuff from the other three as well.
If you want something short just for starters, you can also try Profit & Loss.
Also, another fantastic book for those just starting out is The Anti-Capitalistic Mentality.