to open your file in notepad++ automatically, just pass it to notepad++:
"C:\Program Files (x86)\Notepad++\notepad++.exe" "D:\path of file\file.log"
To have it update automatically, this answer has been answered already in SU: How to automatically reload modified files in Notepad++
Settings -> Preferences -> MISC -> Update silently
There is a nice plugin called Document monitor (Can be found and installed from the Plugins => Plugin Manager => show Plugin Manager menu),
It updates the opened files every 3 seconds. Together with the option to "scroll to last line after update", it will have the ability to "tail" a log file as wanted.
After the plugin installation don't forget to activate it by clicking:
Plugins => Document monitor => start to monitor