Welcome!

1) Can be a variety of reasons as already mentioned, from low battery/charging system voltage, to sensors, to more expensive parts. A search will give you tips to narrow it down.

2) You have a good mechanic, yes that is a common cause of camber that cannot be adjusted to spec. Self levelling suspension can be at the proper height and you can still have excess camber if the bushes are worn.

3) Usually the transfer pump between the 2 halves of the fuel tank. You can monitor the left/ right fuel tanks using your instrument cluster test, #5 IIRC. Search for unlocking intrument cluster tests to get the procedure to unlock access the tests.

__________________
04 X5 3.0i auto
03 X5 4.6is