IMDEN Bluetooth 6.0 FM Transmitter for Car, MP3 Music Player Wireless Radio Adapter Kit with QC 3.0 Fast Charger, Hands-Free Calling, Supports USB Drive for 12V/24V Vehicles

Use a low power FM transmitter with an integrated bluetooth receiver. I have this one that I used in my older car. https://www.amazon.com/dp/B07F2RTN5Z

2 and 3 are easy diys. Someone already gave a good answer. I'll say for 2 though, if the radio works and you have a standard 12v car plug you can just get one of those 12v bluetooth radios. Much cheaper and no installation needed. Audio won't be quite as good as if you replaced the stereo head with a bluteooth capable one, but they're pretty acceptable quality in my opinion (my wife calls me an audio snob and they are good enough for me). They plug in your 12v socket, you pair your phone to it by bluetooth, set it to an unused frequency in your area, it broadcasts that over radio, you tap into that with your cars radio. Something like this (I'm not advocating this product specifically, my model is no longer sold, just giving you an idea) https://www.amazon.com/IMDEN-bluetooth-transmitter-Wireless-Hands-Free/dp/B07F2RTN5Z/ref=sr_1_2_sspa?crid=107BFE6BI2XK&dib=eyJ2IjoiMSJ9.CdKjBFBpd5DhyAWPo9T9WuMubFB-v_FAU3LmQsdZoeWu63Ty_mRqZAzIDZuA0sSftgB0MHbAGzuBzCNTz6cqSrPE3XJO-1zyNFZgYP3qWSTZqf9FGmu2Nb56qdqQB2xZXwYoTEQpEu6Qz_dapDur5gWWL1ns_AXNRfBMPkXEvt9m0zLpEnJoXJzxvtlgLD3560FJVS0PHzUwTTvND6r-7L9aTsqRdpaod3j87oe05rw.RXvuYN54ipdq2GCcXtXpEdzy-wm5M4ao-hfmG8E5u7o&dib_tag=se&keywords=12v+bluetooth+radio&qid=1782179985&refinements=p_72%3A1248879011&rnid=1248877011&sprefix=12v+bluetooth+radio%2Caps%2C130&sr=8-2-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1