If you do a search through the forum, you'll find loads of posts on this. Just take a few minutes to look.
Theres no major issues with this engine, it's strong, powerful and reliable. The inlet flap problem is relatively minor and you don't need to worry too much about it. Again, there is a really long past thread relating to it.
Mpg wise, again it's been gone over time and time again if you search. Real world average 32-35. Some people claim more but even Audi techs have told me anything over 30mpg is good.
I can highly recommend getting one, as will all the other 3.0 owners on here.