I bought my V70 from its only owner, a Yale professor, back in 2016. Then it had about 248k miles - now it is up to 278k. It has been great to me in the past 4-5 years with limited issues - I mean, I paid $1800 for it. Best of all - manual transmission. I was able to handle a few quirks from advice here (taillight issue which ended up being a relay recall issue as I discovered though not an actual recall with my VIN).

So - now I have the following issues and want to address them in proper order. Any advice would be great.

Engine revs up or revs then dips suddenly, especially stopped at lights, to the point it might sty at 3k RPM or dip down to near 0 - usually it is steady stopped at 1k. Mechanic said it was likely the accelerator pedal sensor.

Alarm system service light. I mean, I have only experienced the flashing lights as an alarm. Can I get rid of this - don't need it? Can non-Volvo mechanic clear it?

ABS service needed. Same here as above?

Check Engine - o2 sensor and catalytic converter. What to do?

Strange battery drain. Picked up a piece of furniture on CL and had car parked with hazards on. Battery died in 5 min. Happened once before when I had key on position 2 with radio on while I cleaned out car for 5-10 minutes. Once it stalled at a stop light - could be related to my first issue above?

And what items should I be checking in on at this point? At 278k, I have only put on 30k in 4-5 years. City person here/not daily driver. Always checking fluids/oil.