How-to migrate from "Blue Pill" STM32F103C8T6 to stand-alone MCU?
The Blue Pill (BP) uses two mpu lines as direct USB interface (PA11, PA12) . 

There are numerous BP schematics on web eg vast numbers here

Here is an excellent BP discussion that is likely to be useful.

This SE EE Q&amp;A How to program custom STM32F103 board discusses a cloning attempt.

This page discusses a BP superset that is liable to provide some useful ideas. 
Super Blue Pill — Like STM32 Blue Pill, But Better!. USB is still on PA11, PA12 -  USB hardware consists of 3 resistors :-) !

Schematic of "Super Blue Pill"