How to brown the sugar for pumpkin flan?
A medium saucepan would probably be in the 8-10 inch range.

Your sugar isn't colouring because the heat isn't high enough or it's high enough but not long enough. Just keep cooking, the change will happen. You can try less water but if you're not familiar with working with sugar, better to err on the side of caution; I do work with caramels a lot, and when I know I'm liable to get distracted by other things I have on the go I purposefully use more water than needed to give myself breathing room. 

Are you using the correct size of dish as specified by the recipe? Some of the caramel will dissolve into the filling as you pour it in and as it cooks; I wouldn't worry about the thickness at this stage.

Beyond that, I would personally stay far, far away from anything done by RR. I don't criticise cooks lightly, and I generally try to cook some of their recipes before I'll pass judgement. The recipes of hers that I have tried, both from 30 minute meals and the website, are uniformly awful. Poorly written, ingredient quantities are off, and generally they just taste nasty.