If you could be more specific wrts to yr budget we could suggest better.
If your budget allows, mininum go for the 523i 2006 above. reason being after 2006 E60s come with push start.
Better if you can stretch to post 2007 as I think most by then come with pilot gear stick and some come with HUD (heads up display).
For me I would look for local cars (AB,Ingress,Quill,Sapura etc) as we can always trace their history and 99% rust free except if the had been involved in accident before (minor ones also).
Japs spec will come with a different FM frequency range, I like to listen to the radios so this is no-no for me. You can't get freq more than 90MHz (correct me if I am wrong) so no Hitzfm or mixfm for you guys
On the side Japs spec normally tend to have lower mileage,less or no rust and perhaps cheaper due to lower import tax (special Msia-Jap agreement I think to boost trade).
UK specs tend to have more rust and higher mileage and the odometers are in MPH. Most dealers unfortunately clocked (tamper) the odometer to make the car look low mileage.But no issues with radio reception as the UK uses the same frequency as Mysia.
Cheers