I have selected some variables from the data, and for a category variable, if it contains N categories, I will set up N-1 dummy variables for it, if so, there are 26 variables in my model, is it too many for a model?

But if I just treat the category variable as factor, the number of variable would be about 15, it seems ok for a linear regression or logistic regression, but I am not sure if it is ok for a cox model since I never use it before.

Anybody can give me some advice?

Many thanks!