MPG can drop to about 20 or just under when town driving, but over 30 when M-way crusing. For mixed driving you should average around 25mpg.
Tyres - all depends how hard you thrash them. Changed mine at about 11k or 12k. Rears were pretty well gone, fronts still had a bit of life, but I wanted the same on all 4 corners so changed them all at once ( about £550 for Toyo T1-Rs, which are highlt recommended ).
I'm sure there's a thread explaining the differences with JDMs somewhere. BAsically the early ones were inferior in quite a few areas, the later ones are more or less the same, so depends on how old you were looking at.
No major faults - a few smaller things fitted under warranty ( although I've not needed any of them ).
Have you had a test drive, if not, give it a go, bet you'll be impressed
Gus