Q: Deleting Music from iPhone (impact on...)

There is no risk of any music being deleted on your PC if you deleted music on your iPhone. Music from your PC will only be deleted if you purposely drag the music into the Recycle Bin

Only if you have "Sync Music" checked in the music tab under your iPhone in iTunes. See this for more info: Sync media between your iPhone, iPad, or iPod touch and iTunes on your Mac or PC - Apple Support

Just sync the music from iTunes using:

Sync your iPhone, iPad, or iPod touch with iTunes on your computer using USB - Apple Support

If you are really that concerned about losing your iTunes music library, you should make a backup copy of it:

Manage and back up your iTunes media library - Apple Support

Music sync is one way, from computer to iPhone. Nothing you do on the phone will affect the music in your iTunes library on your computer. The easiest way to copy music from iTunes to your phone is to create a playlist in iTunes, drag all of the music you want on the phone to this playlist, then click on the iPhone icon in iTunes, go to the Music tab, select this playlist, then click Sync. Any time you want to change the music on your iPhone just edit the playlist to add or remove content, and sync again.