You want the 500a shunt not the 100a so when you get the 2000w inverter that is coming next :) you can pull over a 100a and have no issues.
Some places sell the Tri with everything, and some sell the items separately. If you use the 500a shunt as your buss/junction, be aware the bolts in the shunt are quite short and can only hold a few ring lugs stacked at a time, so you might still want the buss/junction to have more places to put ring lugs.
The solar controller that goes with the Tri has a shunt too ISTR and it gets convoluted for sharing shunts and all that. Was a thread about this recently. You are probably ok with the controller you have.
#8 to the roof should be fine, but you will be able to tell once you are out in the sun and check the controller's display for "expected amps"