Need help with engine error codes on 99 Boxster

[Pianohawk]

I have the following engine error P-codes:

P0102 (Mass air flow sensor, short to ground/below lower limit/ lean mixture threshold)

P1124 (fuel pump relay output stage, short to ground/below lower limit/lean mixture)

P1126 (oxygen sensing adaptation, lower load range, cyl. 1-3, short to B+/above upper limit/ rich mixture threshold.)

I would be immensely grateful to anyone who has ideas on where to start. Thank you soooo much!

Colby