This is interesting advice given that you haven't kept a JD...just saying.So, I have never had a JD before, but I do have 9 Tiger Barbs in with a BA in a 29 gallon, and knowing what I do about JDs I would say that the Tiger Barbs and the Jack would be fine. I mean you would just have to provide enough cover for them to hide. Tiger Barbs defiantly know how to take care of themselves.
Also, With the mixing of the GT and JD, it is hit and miss. Each fish has it's own personality and mix differently with different fish; could work, but also could fail miserably. If you do decide to do it, I would make sure you have a plan for one of them just in case is doesn't work out.
A BA is a Blue Acara. I wouldn't recommend them for Jacks. They aren't mean enough or big enough to deal with one. Convicts might work if you want something of similar size.This is interesting advice given that you haven't kept a JD...just saying.
What is a BA?