For the car window stuff, I’d recommend a GoPro type camera, or putting it on the dashboard. I remember I shot in a car once and I had a gopro suction cupped to the windshield and I was under the passenger seat (not in frame) running audio.
You may have to think about re-adjusting your vision if you can’t rig it up safely and if you don’t want to spend the money to make it safe. You can possibly find some interesting workarounds to get a similar result!
For walk and talks? You can check out some cheap stabilizers like the Roxant Pro (I can’t get that thing balanced for the life of me so I am at odds with it at the moment.). You could try some tripod wheels but you’d need a track so you can make sure the surface is smooth (it doesn’t do well when the floors have any sort of imperfection which makes it tough.
Let me know if you have any follow up questions!