Hi all, I'd love the advice of any locals (or any expert) on this

I'm flying on a UA redemption ticket from Brazil in to IAD. From there I will need to buy a domestic revenue ticket to get down to Florida.

My flight is due to arrive at Dulles at 6.30am. I am looking at catching a US Air flight out of Dulles at 9.18am. Would I have time to clear immigration/customs, pick up my bag and check in again? Note: I hold a US passport, if that makes any difference.

In my mind I worry I'm cutting it a bit fine. There is a slightly later flight available on ebookers, but I have this United voucher to use so feel like I may as well spend it. Frustratingly, the slightly later flight doesn't appear on united.com

How much time should one allow to enter the USA from abroad at Dulles? I'm guessing if I miss my connection, I'll have to buy a rather pricey one there and then. But it wouldn't automatically cancel my return flight right?

I'm starting to think maybe I should just fly with carry on, maybe it'll give me more chance!

Thanks!