I assume you have the T-stick for your 4-way joystick and the 2 competitions are your P1 & P2 8 ways?
I would ditch the T-stick and go with a Happ 4-way MsPacman/Galaga reunion stick. This is a better 4-way solution and is closer in feel to the other joysticks on your panel. The T-stick throw is too completely different from the Competitions. I speak from experience because I originally did exactly what you are doing and replaced my T-stick plus with a 4-way reunion stick.
SlikStik Tornado already comes with a Ps2/USB combo cable, so it plugs straight into your motherboard, not the Minipac. My preference would be to get the PS2/USB trackball and use the regular Ipac. This would elminate the Optipac and give you screw terminals on your keyboard encoder. You also don't have to worry about a harness to connect the minipac to the trackball. It costs a little more, but gives you the most flexibility.
I have all the parts mentioned above (Ipac, minipac, PS2/USB trackball, Tornado Spinner), so these opinions are based actual use.
I also agree that I would ditch the 5 buttons dedicated to mouse/trackball.