Sweeten to taste: add more dates or omit them depending on how sweet you like your drinks. Your cherries or bananas might be very sweet and then you might not want dates, or you may need more to balance out the cocoa, depending on personal preference.
Freeze it for later: if you happen to end up with too much smoothie and aren't sure what to do with it, you can freeze this (and any smoothie) in ice cube trays. When you're ready to drink it, simply blend with enough milk to reconstitute into a smoothie - don't thaw it.
Cocoa: dutch process cocoa is a little smoother and milder. Use natural cocoa if you prefer a slightly more bitter taste. One or the other will change the smoothie colour (you can see this here - the step-by-step photo was with dutch process, and the picture above was with natural).