Welcome highland!
Glad to have you on the Quilt Board! I'm sure you will get a lot of help and suggestions from the marvelous people here.
If you haven't cut all of your blocks I would really recommend cutting bigger blocks. Because of the thickness, denim has it's own set of challenges to work with, a few I can think of: you'll need a denim needle for one, maybe a heavier thread, a wider seam allowance because of fraying, and the weight of the quilt will be much heavier than your normal quilt.
If you have already cut your blocks and your cut size is three inches, then you can figure 2.5 for a finished block (seems small for a denim block), so 70" (width) divided by 2.5" = 28 and 95" length divided by 2.5" = 38 ....28 x 38 = 1064 blocks. However...because it's denim some would recommend using a wider seam allowance in which case the blocks would be smaller and you would need more to get your finished size. Something else to consider, rather than all denim, mix it with quilting cottons or flannel.
These are just some of my thoughts and I'm sure you will get many more from others more experienced than I.