[200q20v] 7 Error codes - what's next?

[Jagernauth, Stephen, BMSLS]

Since my check engine light has been coming on intermittently, I got
around to dumping error codes.  Got 7 codes in the following order:
2112 - Timing/TDC sensor
2324 - MAF sensor
2111 - RPM sensor
2341 - O2 sensor limit
2231 - ISV
2113 - Hall sensor
2342 - bad O2 sensor

I have 125k on the car, purchased with 89k and suspect it's
the original O2 sensor so will change O2 but is it possible these
codes are inter-related, i.e. 1 problem is causing the other codes?
I'm not in limp-home mode so the 2324 is suspect.  I may have a
slight exhaust leak with a car of this mileage and original exhaust
but nothing obvious.  There may also be an air leak since most of
the hoses appear to be original.  Any tips on a logical order to
diagnose short of just changing everything?

Regards,

Steve Jagernauth sjagernauth at att.com
'91 200TQ