However, my thoughts are that copying someone else's chords will help me practice and become a better player, but to learn the theory will require knowing why and how, I suppose. No, I'm afraid I hadn't heard of the ii7, V7 you mentioned.
Don't know if it's of any interest, but I took a screen grab of my piano roll. I wanted to make different chords joining the main ones. There may be some logic that I've stumbled upon, but it was all just guess-work and using my ears to determine if I did or didn't like it.
I'll shut up now. I feel I'm repteating myself and I have already taken up too much of all your valuable time.
Thank you all, once again,