Is there any way or sense in which God is necessary?
A great question Sunstone. To my simple mind, true knowledge is the ability to ask good questions and not necessarily obtaining good answers, after all the latter is directly dependant on the former. To answer your question, sadly for theists, the answer is no, although "god" answers many questions for some who cannot understand reality in any other way. In that sense "god" is their necessary projection.
For instance, is God necessary to explain anything about the universe?
Again, No. The physical universe can be described rather well without the need to tie "god" to the back of the Jimmy and drag "him" down the garden path. Bringing "god" into the mix certainly does provide us with entertaining stories to tell our children and those who are as children however.
Is God necessary to make life meaningful?
Theoretically one could find deep meaning in an ashtray or a jar of mixed nuts. The human animal attaches meaning to whatever it thinks is somehow reasonable.
Is God necessary to underpin morality?
No. Why would anyone think that they need a "god" concept in order to tell them how to live? In theory, even a fence post ought to be able to figure out how to survive just by paying attention to life itself. Again, there is no need to bolt "god" to a tree and then blissfully offer prayers to his rotting corpse with the hope it will make someone what they can't let themselves be on their own.
Or, is God necessary for some other reason?
In reality, no, however that does not mean that many find the concept comforting and so in that way it is indeed necessary. Mind you so are air and sunlight.
If God is in any way or sense necessary, in what way or sense is He necessary? And why is He necessary?
God concepts are necessary as a catch all to explain our "unknown" but sensed reality. God concepts are designed for those who cannot directly understand the true nature of reality which is indeed a few jumps ahead of such timid, self-serving concepts. Here I am reminded of how we teach little children about Santa Claus. It fills them with wonder and no small sense of awe, but all the while we understand that one day they will learn the truth.