Personally I would avoid the 1.4, father in law says his is way underpowered.
We have 3 mk5's in our exrended family 2004 1.8 Design auto. 2009 1.8 Life auto. and 2009 1.4 club manual.
All have proven to be utterly reliable with no issues at all bar routine servicing. Some people report interior plastic can break easily although I have found it to be quite robust compared to facelift Omega interior.
That all said the highest mileage on our Astras is the 2004 one with 43k miles on it. There can be issuse with the autos. Standard auto have a weak radiator seal and can fill the autobox with water. The funny manual/auto box (cant think what its called at the moment) has plenty of issues.
1.8 heavy on fuel, i get around 29mpg around town 30 and 40 mph roads, better on a run.
Buy the best model you can afford, Design or Elite, only difference is Elite has leather seats which are not as comfortable as the Designs half leather seats.
If you can find one with CD70 factory sat nav is nice and not that easy to retrofit.
Base models like Life have no additional wiring looms for adding extras like heated door mirrors, this can also effect sport models like SRi, If looking at5 door models only the Design and Elite have rear electric windows.
The wifes Design model has loads of extras auto headlights auto wipers auto dimming mirror LEDs in the internal door handles headlights that stay on for a bit when you get home, nice touch that IMHO. rear reading lights andprobably others I cant think of at the moment.
My Life model on the other hand has none of that except the headlight stay on thing.
Some peoplelike XP bodykit it is the factory fit kit and is a personal thing wether you like it or not, to me it just more expensive bodywork repairs
2004 1.8 (125bhp)auto is higher road tax band than 2009 (140bhp) auto