I knit an afghan with size 50 needles and 4 strands of Homespun yarn together. I've made 6 of them altogether. They come out nice and soft. I used 8 skeins for each one, but watch out with yardage. Homespun has 185 yards in each skein and your Red Heart has less.
Anything knit with size 50s works up VERY quickly. I have yet to find any point protectors that big, so what I did was wrap a thick rubber band around the ends every time I put the needles down. It kept the stitches from falling off the ends!