I am new to c#, so I would appreciate if someone could quickly point me to documentation on how to write/read files in WL5/c#. Do the Wl4 function (FileWrite etc) still work?
Is there any documentation on all function/objects available in WL5 (the Quick Reference does not seem to have all descriptions?)

QUOTE:
Do the Wl4 function (FileWrite etc) still work?

No (unless you use WealthScript Translator). Here's the answer from our Wealth-Lab 5 Wiki FAQ > An equivalent WealthScript function can't be found:

QUOTE:
If you can't find an equivalent WealthScript function in WL5, think .NET instead.

See the rest of the FAQ for the pointers to the "new names" of some frequently asked functions e.g. FileWrite.

QUOTE:
Is there any documentation on all function/objects available in WL5 (the Quick Reference does not seem to have all descriptions?)

Frankly, we answered this many times over these years on the forum. If you found some undocumented method/object or interface while using Visual Studio Object Browser, then it's left undocumented for a reason (i.e., not a use case as per Fidelity decision). If you're looking for how to do math, file and/or string operations in Wealth-Lab 5, this will also not be covered by the QuickRef: Wealth-Lab 5 speaks pure C#, so any C# book or reference will provide lots of examples which can be instantly applied to your WealthScript strategies. The world just doesn't need another C# reference, and we decided not to reinvent the wheel. But the good thing is the ability to apply a code snippet found e.g. on DotNetPerls, in WL5.