I myself don't have an Ipaq, but do run Opie (
OZ to be more specific) on my Zaurus, but maybe my experiences will help you anyway.
Opie is a fairly slick and easy-to-use interface. it's pretty easy to configure the appearance, and with the Linux console you can get into pretty much anything you want to change around (once you figure out how it's structured).
regarding you specific questions.
*I don't personally use Outlook, so I'm not help with that one.
*I don't really transfer files between my Z and my PC. If I need to d/l something I simply d/l it directly to my handheld as I use a wireless LAN card. Or if there's the situation where I need to transfer a file from my PC on my handheld or vice versa (mostly mp3s), I have a card reader connected to my desktop, which transfers files to a CF or SD card, and then I can open them on the Z. this is really fast and simple, and I don't need to mess with those silly cradles.
*I use a Linksys WCF12, and you can tell from above that it works. It works flawlessly.
*Again, you can tell from above that the CF card works without trouble.
This doesn't really answer any questions about the other options you listed, but hopefully it helps.
And just for the record, when it comes to a handheld, it seems that screenshots can tell a lot about functionality, so check 'em out and see what you like.