Disclaimer: I am not a pro lol. Only had my 450D around 6 months or so?!
How long is a piece of string. Do you want to go out walking and take pictures of landscapes, animals, insects, people etc...
The kit lens kept me occupied for the first 3/4 months and still takes some fab snaps. Then I invested in a prime 50mm 1.8, invaluable tool and has taught me a lot about my camera. Now I want some more reach in the form of a 70-200 but also have a nagging for something around the 10-12mm range and an upgraded 24-70 kit lens replacement.
I'd say spend time enjoying taking photos and if you start finding you want to learn more and challenge yourself etc.. then spend then money upgrading when you have found out what exactly you want. It is a very expensive "hobby" lol!
Oh and the guides in here are brilliant
Happy snapping!