2006 Lexus GS300

Car is having some weird electrical issues:

-The door locks when using the FOB and the switch inside the car seem to work intermittently. So I have to use the key built into the FOB to unlock the driver side door to get into the car, which sets of the alarm. I removed the fuse for the horn, but there must be a secondary horn or something that is still going off. Not sure what fuse to pull? I just want the alarm to not go off every time while I try to fix these issues and still have to drive the car daily.
- The stereo doesn't work. The display works, all functions work, but no audio is coming from any of the speakers

Also... the car is missing its rear view mirror. I'm wondering if there is maybe some electrical components in that mirror that may be triggering the alarm/anti theft and giving me these issues?

Replaced the battery in the FOB, checked fuses, that's about the extent of my electrical knowledge. The car was sitting all winter and needed a jump start, I'm wondering if maybe the battery is just weak and is causing some electrical components to not work? Car starts just fine with the battery as is now though.

Any pointers or places to start diagnosing would be appreciated