Learning any musical instrument properly is difficult. I found it difficult to learn to play but not “hard” because it was something I'd always wanted to do and that I enjoyed. I was self-taught so my progress, especially to begin with, was slow but I still spent almost all of my free time struggling with it. Like I say though, I actually enjoyed it!
Instruments like violin, viola, cell, brass instruments and piano are “harder” but anyone claiming that guitar is easy is mistaken. It takes a lot of time and effort.
Since, like many people of my generation,I'm self-taught I couldn't really claim that lessons are essential but lessons from a good teacher are DEFINITELY the easiest way to learn - the only “shortcut” I know of.
Already being able to read music won't be a help when you start but willbe an advantage later on. The difficult thing though is being able to find the notes on the guitar.