Well if your primary concern is emails, then I would very much suggest a Blackberry, I have been using blackberrys for 3 years now and nothing comes close to what those guys at RIM do,

Regarding google maps, google should out a map version for maemo soon, so that should be ok, also I hear Navteq a Nokia subsidy is planning to get its GPS services on the N900, so that should take care of that

I have no idea about your third question I m afraid, prolly some of the other guys could answer that.