Hi..
Interesting project.
I already done similar project like this, with different approach.
The good news is raspberry pi onboard wifi can be used both as access point and wifi client at the same time.
In my case :
First, i create simple web page in raspberry pi , basically, to scan nearby wifi, and there is form to select scanned wifi access point, and input wifi password.
Second, i create access point in raspberry pi, using virtual access point interface. So, device with wifi will be able to connect to raspberry pi and access the raspberry pi wifi client setup page.
Because of limitation of bluetooth functionality (i think the best is using bluetooth serial communication, thats mean a whole lot programming in raspberry pi, only to set wifi credential), i think this method worth to try. And also, experiencing my previous project, utilising pi’s bluetooth, i can tell the onboard bluetooth is very unstable, sometimes i need to reboot several times in order to make pi’s bluetooth viable. Strange behaviour.
However, please let me know if you are interested in this method.
Thank you and have a good day..