Dang, I paid good money, some stressful days and a little blood, to learn that!!! You mean I could have come here and learned for free? What a deal.
1.) Measure, measure, measure, then measure again. A popped chalk line for referrence works for me.
2.) Blind nail where you can, or glue them, just right there, since there won't be much in the width, with a foot or two.
3.) Yes, use asphalt impregnated felt. It is to keep wood to wood squeaks in check, along with humidity differences between the basement and the living space.
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