One of the major mistakes you can do when starting to learn a foreign language is to translate everything back into your native language. This means there will always be a delay in your speech. It could also mean lots of errors are introduced due to different grammar, possession, word order etc.
If you learn pronunciation first before meaning then you will learn what you are reading in your target language rather than your native language. This will help enormously with your comprehension and communication.
However when learning a language like Greek, finding something with subtitles to go along with your audiobook is like finding a needle in a haystack. YouTube has plenty of music videos, audiobooks, news reports, chat shows etc but very rarely do they come with closed captioning. Overdrive is an app that you can use to get access to digital resources from your local library but they don’t tend to have foreign books. They have umpteen language courses but if you want something relaxing you are again stuck. Overdrive allows you to have multiple libraries stored in your app so you have access to a wide variety of resources and they have a new app called Libby too. This however does not fix your problem. So I suggest going onto EBay to buy a Greek version of Harry Potter to go along with the audio book that is on YouTube. Victoria Hislop is another idea along with Nikos Kazantzakis and The Little Prince.