They come stock with 4" fronts and 6x9 or similar in the rear parcel tray. If you are skilled enough you can fit 6" in the front as I have.
Problems:
Turbo smoking after 150k on the clock
Stock suspension is a bit spongy, but if you want a daily driver it will be fine tho the standard ride height leaves a lot to be desired
PCV Valve clogging (been thru 3 so far but cheap as chips to buy)
Clutches
Gearbox tho I've had no issues with mine in the last 4 years
Manifold tends to crack if you pump too much boost thru it, tho mine hasnt yet and im running 17psi
Valve stem seals need replacing after around 160k on the clock
Cat converter, get rid of it or replace the whole pipe (better option)
No rust yet (touch wood) and it sits outside in the Welly wind every night.
Fuel wise before I moded my car I could get from St Johns in Aucks to Kawakawa in the Bay of Islands and back again on a single tank
Now with the mods I get around 450km out of a tank (open road driving) 360-380km city daily driving.
I love my little starlie and even tho Im looking at buying a new car I've decided to keep it for longer.
Hope this helps