How can we have the volume level automatically change to a set level (that the user picks during app setup) when the app opens?

Question

So a user opens the app and the volume level automatically changes to a level which the user initially picks during the setup of the app.

Additionally, could the volume level be picked for both headphone and non-headphone use, i.e. a volume level for when headphones are inserted in the jack and a volume level when the headphone are not in the jack.