I'm planning to buy a SE X10. Should I buy AP or ORI set? Because the price difference is about RM400.

I planned to buy AP set but I want to clarify something:
Can I update the firmware?
What is the problem if the IMEI no doesn't match the box?
Which AP company should I get it from?
How do I know whether the accessories are genuine or third party?
Where can I find a trusted seller?