My esthetician suggest a 0.5ml top up of Juvederm in my lips. Would 1ml be too much?

This is difficult to answer without photos, but you can get a touch-up of Juvederm to get your desired results. I prefer to use a micro cannula to inject the lips to prevent bruising.  
I hope this helps. 

Thank you for your question.  It is difficult to comment on your case without seeing photographs.  Depending on your goals and expectations, 1 ml might be recommended to achieve your desired result.  Beautiful and natural results can be achieved.  Please be sure to see an expert injector for an in-person consultation to fully discuss your goals and expectations in order to determine the best treatment plan.  Hope this helps and best wishes! 

My advice is to stay within the constraints of your own physique. If you feel you need more, 1/2 of Juvederm syringe could be enough; a full syringe may be too much. Remember, it is not a matter of volume; the goal is a lift and eversion and these can be achieved on anyone with much less than 1 syringe.There is only a tiny gap between natural and ridiculous. It seems to me your perception is very appropriate; you can always add more. Good luck!