Hi Mark

I went through Fundamentals when I joined back in '19 but everything was new to me. I don't want to discourage you from looking at it, but you already have some working knowledge of guitar and may find it boring. However, it may be worth checking out. 

I think as an engineer delving into music theory would come easy to you and if Christopher reads this, I am sure he will, he could outline some lessons that are buried in the vault. 

If there were two things that really helped me in my pursuit, one would be learning to write a song, chord structure and solo bits, this is where theory comes in and two would be joining with other players. Which took some time but now we have a little group. The main benefit, I think from joining the group has been that there are expectations from each one of us that we will learn the material that we want to play. This keeps progress moving forward into new genres of music, because we don't all like the same things. But music is still music and playing music with others is a wonderful experience. 

In regards to bass and guitar, I actually do both, because sometimes I am the bass player. But depending upon how deep you want to go into bass will determine how much time you want to commit to it. My purpose for playing bass is to provide the back beat for the group and I leave it at. I don't do any kind of artist studies into the various bass players like I do with guitar players like Stevie Ray Vaughan as an example. 

Best of luck with it 

Bill

Edit: I should have mentioned that if you do want to be in a band, something that we don't talk about enough is the importance of rhythm playing. That will be critical to play well with others.