Welcome to iPaqHQ!
That's a whole lot in that post.
As far as getting items aftermarket I would check for reviews first before spending money just to make sure that it will indeed work for you.
I can't speak for the h5555 as I have a h2215 but I have the thumboard for it and it works great. I use it mostly for surfing on mobile sites such as this site here.
For a camera you should be able to use any SDIO camera that supports the Pocket PC.
For a GPS system, you have your pick of a CF GPS, SDIO GPS or a Bluetooth GPS. To use a CF GPS you would need a sleeve. Bluetooth GPS is something that I believe is the way to go.