It takes 198 emblems to fill 19 nodes on a 3 star, which is about 8 nodes for a 4 star: Deciding where to spend your class emblems - Tourney update 2019-Mar [Math, Analysis]
What I do is put some emblems on the 3 stars I like (up to 5 nodes, more if I don’t have a better hero in that class). The rest of the emblems are saved for the 4 star heroes.