I've got one in black 07 plate and we love it its awesome. The noise form the 5 cylinder when fitted with a decat is epic. Mines mapped aswell and had no issues as of yet only a missfire which turned out to be the injector connections which cost me £10 to fix for some new connectors from pumaspeed. I might have just developed a driveshaft wobble but to be honest it's not that expensive to get parts for these so I wouldn't worry just get one that's got full service history and not off a yobbo. Same with buying any car. The liner issue well any engine in any car can go pop and from what I've read it's most that are at or over 300bhp.
It's a good solid car I'd be happy to keep for years and that's good for me as Ibe had over 300 cars and I'm not a dealer lol I just like to swap and change, from what I've seen 6k will get you a good one around 2007 I also think after 57 they sorted the liner issue.
Mpg we get around 60miles to £20 so ain't that bad I only get 50 from £20 in my fiesta rs lol