I'm not an expert in this software, but I'll try to help.
1) Instead of an "enum", try the "combo box". The enum, as in most languages, is fixed at compile time. Its value is an integer that the program knows how to interpret. A combo box, on the other hand, is a string data type. You can populate it with strings that you can then select from. You will need to create a diagram reference to the combo box, and then you can use a property node to set its "ItemsAndValues".
2) Listing a folder on the network is a bit more problematic. Access to filesystems is a bit more structured inside a web browser. A malicious web page shouldn't be able to read your entire hard disk and upload it to a server somewhere. There are some web APIs for accessing files, but I don't know what works with the G Web Development Software. Perhaps one of the experts can comment.
I hope this at least gets you a little closer to a solution. Good luck!