Hello Luis, I can recommend you Memrise http://www.hau.gr/?i=learning.en.podcasts-in-greek For learning new vocabulary you can use the WordReference as a dictionary Greek: An Essential Grammar of the Modern Language (Routledge Essential Grammars) this is a good grammar I hope that helps you. If you have any further queries, let me know it.

Hello I have a channel on youtube with greek lessons for begginers. Look for alexandra4edu. I am open to help you.

As a learner myself, I can't recommend Language Transfer enough. It doesn't help with reading and writing, but I find those to come pretty quickly with Duolingo, except for spelling. https://www.languagetransfer.org/complete-greek

I agree with Penelope about Memrise and WordReference . I also recommend this video on how to write the Greek alphabet: https://www.youtube.com/watch?v=JgRYrzc8cFg If you want to, you can practice writing it on a piece of paper, take a photo of it and send it to me for some feedback. I would be glad to help you with it :) When I started learning Hiragana and Katakana I found that games can really help to memorize things quickly. They have many games here: https://www.sporcle.com/search/quizzes/?p=1&s=greek+alphabet If you want a more specific reccomendation about a game, feel free to contact me :) Have a nice day!