Without seeing it I am not sure what I can suggest on the roof situation, as to the fittings it looks like you have 5 panel kits, and 1 system kit, (assuming the large bag in the lower left of the photo is a system kit, it should probably have 4 seconds of black hose, 1 end plug, 1 end plug with a vacuum breaker valve and 2 pipe fitting adapters, plus clamps and mounting hardware) This is all you would need if you were to install in a single bank of panels with no spacing between each. If you are going to layout something like the above plan, you will need additional hose sections and pipe adapters, plus mounting hardware such as landing points for the straps, you will not need an end plugs or vacuum breakers though, in general you should only have 1 vacuum breaker valve per system. (all of these things should be included in that $59 kit on the ebay link you posted, basically you need 1 of those for each panel that is not directly connected to its neighbor)
For your plumbing run in addition to your assortment of 90 and 45 degree fittings (I assume these are 2 inch white PVC), you will also need some number of 10 ft sections of white Schedule 40 PVC pipe (make sure it is Schedule 40 and not foam core DWV drain pipe, dual rated Schedule 40/DWV is ok). It is also advised to use a check valve on the return line and you will likely want to put a couple of screw in plugs or ball valves with T fittings on both lines so you can drain them in case of freezing. In your mostly flat roof situation I would use 2 inch fittings for at least one side so you could blow the water out with a shop vac, or similar.
Ike