My view is different.
As a first bike, I would rather buy new from a credible bike shop.
At least you know it will be the right size, it will be set up properly for you and you will have the peace of mind of a warranty.
Also, you will build a relationship with the bike shop and you will be more likely to get tips and advice etc.
For your budget, you will get a pretty capable bike which can be upgraded as you go along.