No idea on the sat nav.
Fuel economy is about 1mpg better on the 325 vs 330.
I have a manual. I drove the auto with steptronic anddid not like it. If you are accelerating hard and shift up early, if the car thinks it is too early and it can do better it will override you. Never tried the paddles though.
Servicing costs are astronomical. Find a good non BMW garage to take it to if it is no longer under warranty. Mind you, living in Warrington you are just near Euro Car Parts who sell most BMW OEM parts for about half BMW retail price.
High mileage is not too much of a concern, but look around. With the new 3 series just released prices will drop and expect many E46s on the market over the next few months.