How to choose the dimensions of the input matrix?Graph structure or sequence or?

Question

My data is a string, I first convert it into a graph structure, its adjacent vector dimension is 700×700, and then I embed each character into a feature vector of dimension 28, so the graph convolutional The input dimension is 13.72 million. Is the dimension of my feature vector too large? I can't find any information on how to get the dimensions. The current solution still uses strings, but only one dimension is used, so the dimension of the input matrix is only 700×28, which is much smaller, but I don't know if there are other solutions, I am a novice, thank you