New to x5 few questions

[ajmoritz17]

New 01 X5 4.4 Owner-

Im From Ohio so with winter fast approaching I thought I'd sell my g35 coupe for something a little more practical. I found my 4.4 for 13,000 and offered him 11,500. We settled @ 12,200. It has 74 K Miles on it no navigation. my questions-
1. Can I put a OEM Navigation in it? If So how much will BMW charge?

2. When I get out of car i have to pull the handle twice to get the door open if i don't unlock the doors first is this normal?

3. Engine light goes on and off. the car runs great though i don't really feel like paying for a diagnostic. I took it to autozone and had them plug there machine in it (I realize its not the best way) and got a few codes one of wich being air flow issues... so i traced the tubing to the air filter and one of the clips was not fully clipped and air was leaking through. fixed that and light went away...then came back on..then off....then on? But i do hate looking at warning lights.....the airbag light is on as well.

4. Is it possible to get black window trim? not a big fan of chrome.

Any help would be greatly appreciated
AJ