Having read more of your post Paul, especially about your usage I think you will be fine so don't worry.
First thing to do is just make sure you turn off any automatic updates you don't really need that will eb away on your battery.
So things like the weather updating every 5 minutes or something.
Go into the Android market and download an appkiller too, that way you can easily see whats currently running in the background and turn it off if you don't need it.
Like I said, I was very close to getting this phone, it is very very good, but I would use it more than you and so battery life was one of my key considerations.
You will love it!