OK. If you use triangles which are 3.75" high, and you cut your repeats into 18" strips, you can get about 70 sets. You have 6 yards, so you will get 2 sets of strips, or 140 triangle sets. If you cut your strips sets into 36" widths, you will have a bit less waste, and get an additional 10 sets. This assumes that your yardage is cut exactly square. So figure 140 to 150 hexagons. The hexagons finish at about 6.5" high and 7.5" wide. here's a link to a site where you can print off hexagonal graph paper.
http://incompetech.com/graphpaper/hexagonal/
I would first get some tissue paper and make sure that my math is correct on the number of triangles 6 yards will yield, then use the graph paper to determine what layouts are possible (long & narrow? square-ish?) then calculate the size of the finished item.