NS-2 is essentially a dead project, and you are much better off moving to a newer simulator or emulator. I don't know who put up the website that you linked to above, but it certainly isn't the authors of NS-2 (the original website is https://www.isi.edu/nsnam/ns/).
Some of the possible options for you include NS-3 (the logical successor to NS-2 - it has a graphical front-end called gns3), OMNeT++ (which also has a graphical user interface), or mininet-wifi (which is more of an emulator, but still a very nice option).
Yes. NS-2 / NS-3 is extremely complex and you are on your own with no support. I would recommend NetSim. Information on the IoT/WSN library is available at https://tetcos.com/iot-wsn.html and https://support.tetcos.com/support/solutions/folders/14000105117