My Opinion:
I use the thinnest tissue paper I can find. Usually get it at a big box store and they sell it in boxes of 1000 sheet. BUT I just share with friends. OLD phonebooks (at least 1 yr old to make sure the ink is set) are not bad either.
I personally don't like the extra weight that a fabric adds to the blocks, and dryer sheets are ok, but still pretty darn thick. The idea is to make the Paper Pieced blocks (PP) with the least amount of bulk possible, to avoid quilting issues later.
I make string blocks all the time as leader/enders when sewing other quilt blocks. I sew other blocks to the tops and cut like a HST. I've used them to make star points around a square.
SO go for the gold on your string blocks. Great way to use up your smaller strips and they don't have to be the same width either.