How do I proceed to seriously study Buddhism? I have been sincerely studying Buddhism for the last 6-8 months. 


I have covered most of the famous authors and teachers namely Ajahn Brahm, Thich Nhat Hanh, Bhikkhu Bodhi, Tenzin Palmo, Alan Watts, D.T. Suzuki, Sharnyu Suzuki.
I watched a few youtube videos of Ajahn Brahm to get some idea of Buddhist outlook towards life.
I read most of the books available out there to cover the history of the Buddha written for the beginners. But I am not much interested in the history, specifically the progress of sangha and spread of Buddhism in East. 
I have read a few topics that interest me on this stack.
I completed 2 10 days Vipassana retreat and one-month long Zen retreat which included a mini shesshin.


But now as I see the amount of literature is simply enormous. The Tripitaka, itself is massive. For an e.g., I tried reading an article on 12 nidanas on the wiki but it's difficult to read it that ways. It just feels like information overload. 

Can you guide me how should I proceed from here studying Theravada, Mahayana, and Vajrayana? 

Give an answer based on the school you are following. In your answer also include the source from where to study, for e.g. 'Read about 8 fold path from this website'.  

Please answer in the following format:

Theravada

Study in following order.


4 Noble Truth
8 fold path
10 paramis


Also kindly include the recommended retreat and study centers world over that you know of.

Imagine that I will be studying this dedicatedly for the next 3 years or so. Also, include the online resources and paper books if required.
For those (relatively) new to Buddhism here is what I'd (generally) advise in order:


Read Bikkhu Bodhi's In the Buddha's Words: An Anthology of Discourses from the Pali Canon as this will ground you in the Buddha's own words.
Read HHDL and Thubten Chodron's Buddhism: One Teacher, Many Traditions which will give you a respectful overview of the different traditions extant today and where they agree and where they disagree. Note this book is product of extensive consultation with experts in other traditions and their viewpoints are included. Among those other experts are some that you cite above such as Bikkhu Bodhi, Thich Nhat Hanh.
Find a local community of practitioners and sangha that follow one of the traditions outlined in #2 that fits your interests and predilections. In particular, research the community and the teachers to make sure they are valid. After you've made some investigation you can ask others here which communities do a good job representing the various extant traditions.
Really buckle down and try to understand whichever tradition you've picked in #3 and concentrate on that tradition. Don't go picking different ideas from different traditions until you've first really grokked your own tradition otherwise this will likely lead to a lot of confusion.


I am partial to the Mahayana as taught by the Gelug tradition of Tibetan Buddhism that is authentically taught in the West by the FPMT community and the community at Sravasti Abbey in Washington State. However, there are very good Theravada traditions and teachers and some individuals will be better off with them. Not everyone is the same and you'll have to make your own decisions as what is best for you. Trust yourself to do so.

Hope this helps!