Human psychology. We find it inherently very hard to live in a world ruled by Randomness/Chance, Factors outside of our control and a sense of our own mortality as a consequence of natural ageing (eg. your current crisis :-) Think of it like this; a Child is born into a world populated by "Gods" i.e. its Parents/Society who solve all its problems deterministically. As the Child grows up, the gods turn out to be "False"(i.e. there are problems they cannot solve) which is a huge shock to its worldview and therefore it invents new gods (i.e. Religion) to cope with Reality.

>2, what are it's benefits? vs downsides?

A coping mechanism to live in World ruled by Randomness/Chance and Indifference. The downside is that, taken to extremes one loses touch with Reality and lives in a fantasy world.

>3. why did it evolve and thrive? religion and the notion of a God has staying power. this shouldnt be dismissed.

No reason. It is a consequence of Evolution following a meandering path to give us "Big Brains" one of whose emergent properties is a need to invent God/Religion (see also the book The Runaway Brain: The Evolution of Human uniqueness)

>4.i am not dismissive of Faith as I was when I was younger.(how we change!!) clearly it has its upside. or it wouldnt have survived over the centuries.

No, the above statement is itself an act of Faith :-) Ever since the advent of "Modern Science" starting in the 17th/18th century Faith/Religion/God have lost their Cachet.

>5. what is that comfortable 'sweet spot' where i can have a intersection of the benefits of Faith and Rationalism?

A marriage of Philosophy and Science. For example, i like Samkhya for its model of the World and our Position in it, Yoga for its everyday discipline for keeping Mind and Body in harmony and Scientific Materialism to enjoy the World.

PS: You might also be interested in life arguments put forth by Jack London via his hero Wolf Larsen in the novel The Sea Wolf - https://old.reddit.com/r/books/comments/1jqpar/what_book_sin...