Knitted already other pairs of this pattern at the beginning of the year. Look here:
http://www.ravelry.com/projects/Liatorino/bulky-yarn-booty

The violet pair of these slippers, is knitted with needle 5, double taken yarn and a cast on of 78 stitches.

29-8-2016 : finished the second pair on photo 1 this morning.
The green pair is knitted on needle 6, with 80 stitches casted on.

Started a third pair this afternoon, with needle 6 and 74 st.On photo 2: both knitted with needle 6 and 74 stitches casted on.

3-9-2016: a fifth pair, klnitted with needle 6 and a cast on of 70 stitches.

6-9-2016: 2 other pairs : the left ones with a cast on of 70 st, the blue ones with 74 stitches.