It's great you are getting such a great headstart. By the time you reach 4 years you're going to have tried so many things! You should totally come back to this thread and see how much progress you'll have made :D.
I started with Duolingo, and loved it. It's what brought me joy when I was first learning a language and had no clue what to do when learning a language! As others have mentioned, it's not enough, and to use other tools.
I would suggest that you stop using Duolingo and find a tool that is more efficient and that teaches you material that is RELEVANT to your life. Duolingo doesn't teach you to speak and that's the one of the 4 skills (reading, writing, listening, speaking) that people often put off for a long time.
Next, accept and be prepared for your interest to come and go. You can start with a bundle of energy and intend to do it an hour a day, and 5 hours on weekends. That PROBABLY won't last. Building a habit takes time (of which thankfully you have a lot!), and being consistent is the MOST IMPORTANT THING. So, when your motivation wanes (it's inevitable) in a few weeks, months, whatever, don't stop completely. Reduce it down. Half an hour a day, but keep it every day, for example. Keep it going until it's just something you naturally do. Mix it up too: make sure you're keeping time for speaking practice, and don't keep yourself on apps learning vocab for example.
Personally, having taught myself French to C1 level over the last few YEARS, I've tried a lot of techniques (Duolingo, Memrise, Anki, Quizlet, italki, in person language exchanges...), and I would now recommend you follow something like Benny Lewis' Language Hacking method for a good starting point. I'm not an extrovert like him, but I've realised the importance of getting over a fear of speaking ASAP. It teaches you to speak from the start, and only learn the grammar and vocab YOU need, that is relevant to YOUR life. Most importantly, it shows you you can have a conversation with only a few words. Duolingo teaches you a bunch of useless vocab that you're not gonna use for ages or ever. Why put that in your brain?
Look into the book Fluent Forever, for which an app is in the process of being made. It's a wonderful language learning method based on the science of how the memory works. HOWEVER, it might only be right for you in a few months when you've tried a few things as it's for serious learners.
Drops is the latest craze that is fun and colourful like Duolingo and Memrise but allows you to dismiss words you don't want to learn right now. Again, this is great because you only learn what's relevant to you.
Taking classes on italki changed my life. Often cheaper than a 1 on 1 class in person, and you can do it from the comfort of your own home. I've used it for both structured classes and conversation practice. Now I just do it for fun!
Meetup.com to find language exchange meetups in your area.
Language Hacking book: https://www.amazon.com/Language-Hacking-French-Conversation-Beginners/dp/1473633095/ref=sr_1_1?keywords=language+hacking+french&qid=1554480276&s=gateway&sr=8-1
Fluent Forever: https://www.amazon.com/Fluent-Forever-Learn-Language-Forget/dp/0385348118/ref=sr_1_1?crid=25PI7CK0RP4UH&keywords=fluent+forever&qid=1554480298&s=gateway&sprefix=fluent+forever%2Caps%2C216&sr=8-1
Fluent Forever Creator's TED Talk which is basically the first chapter of the book: https://www.youtube.com/watch?v=iBMfg4WkKL8
Here's hyperpolyglot Luca Lampariello's guide to how to learn a language from scratch: https://www.youtube.com/watch?v=yexczOMlTwI
It probably won't be relevant to you yet but I have a YouTube channel where I talk about the real language that the French use. Once you have a good foundation from your studies my videos could be interesting for you. Plugging myself https://www.youtube.com/watch?v=Xm8ZJnHy0zY.
Good luck and don't worry if this is a lot. You will try a few things and find some that work for you and some that don't. Good idea to reach out to those more experienced. Don't hesitate to ask me any more questions you have. I love this topic.
As you've already identified, the most important skills for you are speaking and understanding. So you need to learn to be able to use it in your profession, primarily. That's what I'm getting from your post.
I fully recommend Benny Lewis' book that is designed to get you speaking from the beginning, and you only learn what grammar and vocab YOU need and not a bunch of unnecessary stuff that can wait til later.
Amazon UK - https://www.amazon.co.uk/dp/1473633095/ref=cm_sw_r_cp_apa_i_W9hUCbRQ7BVE0
Amazon US - https://www.amazon.com/dp/1473633095/ref=cm_sw_r_cp_apa_i_O.hUCbYF33GBV
Amazon France - https://www.amazon.fr/dp/1473633095/ref=cm_sw_r_cp_apa_i_raiUCb0ZGD4JG