I'm not sure about push, but with the data add on you should be able to setup your email client to auto check.

Which email account will you use? I hope you're not considering O2's mail. you'd be better off with gmail or yahoo.

What handset are you going to use?

One thing to note is that O2 3g coverage is limited and I find Edge coverage to be ok, but not great. Certainly you will not get the same coverage as you do with 3.

That seems like a good deal, but don't expect too much data use, I currently use about 50mb a month, although with the iphone I'm crippled to download anything over O2.