Just bought a 1998 2.5L Boxster ----- Code issues - Help please

[1998Boxsterrr]

Hello all. first time poster here. be gentle!
98 Boxster 2.5L

currently, check engine light is on as well as Brake Wear!
have the following codes:

P0138 (O2 sensor)

P0410 (Primary Air pump injection)
P1411 (2ndary injection)

P1124 (Fuel Pump Relay)
P1126 (Fuel Pump Relay)

First off, how common are these issues? Worth repairing? Is it something i can go given limited mechanical experience (but willing to get my hands dirty)?

I bought the O2 sensor and it looks like by taking the wheel off, it's a 10 minute job.....i was also told that the paired codes above are related.

anyways, looking for some general guidance as to what to do and which to approach first.