Battery consumption does depend on the apps and services you use. Google maps or music usually don't consume a lot even with location enabled so a 10k mAh should be enough but it's always nice to have some more.
Using a usb adapter may affect your voltage if you use fast charge, however even cheaper ones handle 10W charging.
And no, any sort of cable is good to charge a powerbank or phone, they can withstand higher voltages but not the phone so they'll deliver less like no problem
So, long story short the anker powerbank gonna charge iphone while using i.e. KOMOOT (bike tracking and recording at same time) EVEN WITH 5W 2A standard cable &&&& apk drainage won't overcome powerbank charging???? - same goes to charging powerbank with standard brick right?
stypid people from stores here be like "brick power should be 18W, whereas the wire should transfer the appropriate electricity. Voltage of powerbank sure is 5V, so the wire should allow electricity transfer 3.6A, so standard 2A cable won't work charging from powerbank wise" - SO THEY LIKE, NOT GONNA CHARGE AT ALL, not even slowly FORGET APK DRAINAGE VS POWERBANK CHARGING JUICE GOING IN.