Thank you @owasco!
I'm hopeful you'll get some stronger eggplant. I don't know how to measure one way or another if an eggplant is a good size and healthy because I have no experience growing them before, same with the squash!
Hopefully the vinegar will help for your pH adjustment and will do the trick, and that vinegar will probably keep those flies away is my guess.
That's a good tip about picking stuff early to promote more production. The small pepper is looking like it might be rotting or something might have got inside of it, not sure but the pepper plants in the back are gaining some decent size so hopefully there will be more.