Thanks Jim, I sort of get what you're saying. I have the 2020 UnltraPak so have the features you mentioned. I guess one of the limitations is that if I put my midi melody on the Melody Track and then try and create that exact melody on the soloist track using a Midi Supertrack as the soloist instrument, I can't do anything like a lead guitar as there are no Midi Supertracks for such an instrument. I'm trying to write modern country orientated music and so a lead guitar riff at the intro and throughout the song is important. I know what I want the exact notes to be and their timing, but creating it is the problem. I'm not after perfection so maybe a VST guitar would be the way to go, and use BIAB for the all the other parts of the song which don't have to be so specific.
I haven't written much for a while, but am looking to write more in the future.
Here's a couple of things I did in a studio and was able to get the riff played as I wanted:

https://soundcloud.com/stevebarnesmusic/in-tune
https://soundcloud.com/stevebarnesmusic/going-home

Getting songs done in a studio is expensive, so if I can get it worked out using BIAB it would be great.