Set up PyCharm for PyQGIS 3 development

Basile, as a P.S. to my comment, my batch file (pyqgis.cmd) looks like this:

@echo off
SET OSGEO4W_ROOT=C:\OSGeo4W64
call "%OSGEO4W_ROOT%"\bin\o4w_env.bat
call "%OSGEO4W_ROOT%"\apps\grass\grass-7.4.0\etc\env.bat
@echo off
path %PATH%;%OSGEO4W_ROOT%\apps\qgis\bin
path %PATH%;%OSGEO4W_ROOT%\apps\grass\grass-7.4.0\lib
path %PATH%;C:\OSGeo4W64\apps\Qt5\bin
path %PATH%;C:\OSGeo4W64\apps\Python36\Scripts

set PYTHONPATH=%PYTHONPATH%;%OSGEO4W_ROOT%\apps\qgis\python
set PYTHONHOME=%OSGEO4W_ROOT%\apps\Python36

set QT_QPA_PLATFORM_PLUGIN_PATH=%OSGEO4W_ROOT%\apps\Qt5\plugins\platforms
set QGIS_PREFIX_PATH=%OSGEO4W_ROOT%\apps\qgis

start "PyCharm Aware QGIS" /B "C:\Program Files\JetBrains\PyCharm Community Edition 2018.1.4\bin\pycharm64.exe" %*
REM cmd.exe /K cd /d "C:\

and my python interpreter is located here:

C:\OSGeo4W64\apps\Python36\python.exe