Be Thankfula Cross Stitch Pattern by Cross-Point Designs

I have had extensive experience XS-ing, but not necessarily in teaching a class. I thought I'd use this leaflet as a teaching tool. So, given the size of the project and the density of the stitching, how do I "guesstimate" the lengths of thread I need to provide to create a kit, if the number of lengths are not listed on the leaflet? (I know..."stitch it first" is the best way, but....I may not have it totally stitched before the class.) Actually, finding proper kit materials is more difficult than it seems. The classes are through the local adult ed, so religious kits may not be appropriate, and therefore Christmas, etc., may not be either. There's one project I've seen that might work" Today is the tomorrow we worried about yesterday" My only concern was how extensive the project is for a first try. Any information/advice would be welcome.