check out this thread
http://forum.ppcgeeks.com/showthread.php?t=72923 seems to address alot of your questions and if you look at post #7 there is a REALLY cool app called sprint mail in cab format. its a push mail app and can only be used with one email acct....but for most thats aplenty! ive had it installed for a few days now and can honestly say i have seen ZERO change in my battery life.
hope this helps....if so hit the thanks