Rob,
I am currently working on a few turorials for Fifth Element costumes, including the Orange Suspender Leeloo costume. Hopefully they go live in late January.
For the suspenders I poured silicone elastic into a form and made my suspenders. But I have also seen a good looking suspender crafted from Yoga floor matting. I do not recommend using orange vinyl cloth for the suspenders, it does not have the thickness to look correct on the wearer.
Boots. Leeloo's boots look to be calf-high military looking boots with a knobby sole. There was a ribbed cuff attached the top of the boot which also had a buckle on the outside which looks to be more decorative that utilitarian.