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Thank you for this. I'm just getting started so additional guidance is much appreciated.

I can only recommend things like going into Prem Nirmal's teachings for understanding as he is the spiritual scientist, his youtube channel https://www.youtube.com/channel/UCFjVDuy4A0zs0enJxOwNkew have over 20 vids he is also on FB and having a blog
http://premnirmal.guru/ also older blog with many important articles like
http://premnirmal.blogspot.co.uk/2010/09/36-elements-of-kashmir-shaivism.html, books like
https://www.amazon.com/Vijnana-Bhairava-Practice-Centering-Awareness/dp/8186569359 for techniques or
https://www.amazon.co.uk/Tripura-Rahasya-Supreme-Perennial-Philosophy/dp/0941532496 for deeper understanding of Life. Also Dzogchen buddhism with it's concept of Rigpa...Rest of it is practice.

There is also Robert Monroe from Monroe Institute on astral travel: