Hi there! Changing OSs can be challenging, but we're here to help! Most of the time, except for iMessage, anything you could do with your iPhone you will be able to do on Android (and then some!).
Music control on the lockscreen is possible (and from the Always On Display, too!). Just play anything and the music 'widget' will appear on the lockscreen (for AOD it's enabled by default, but you can disable it).
As for the font color on the notification bar, it's not as simple. The S9 does have a plethora of themes to choose from that will modify the font color on many elements and even the color of the icons in the quick toggle buttons and navigation bar, but color for the notification bar (where you see the time, battery, and notification icons at the top) cannot be changed (you can change the font, though). However, some apps do allow for that element to be themed, so you can change the color, but most will require root access (the equivalent of jailbreaking on an iPhone). The only app that didn't need root on a Samsung phone (Substratum) no longer works in Android Oreo, so until (and if) they patch that up, only root apps would work.
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