Hi,
Take a look at mine prepare command.
I am doing pretty much the same except I left the icons and the splash screen out.
To save build time on AppCenter use --platform android or --platform ios.
native-builder.exe prepare 
--java-home "C:\Program Files\AdoptOpenJDK\jdk-11.0.3.7-hotspot" 
--mxbuild-path "C:\Program Files\Mendix\8.7.0.1476\modeler\mxbuild.exe" 
--project-path "C:\Users\Contacts\Contacts.mpr" 
--github-access-token "XYZ" 
--appcenter-api-token "ZZZ" 
--project-name "Contacts Native" 
--app-name "Contacts Native" 
--app-identifier "com.mendix.contactsnative" 
--runtime-url "https://contacts.cfapps.eu10.hana.ondemand.com/" 
--mendix-version "8.7.0" 
--platform android