Raised-Cosine Filter - calculating magnitude response
The frequency $f$ is no parameter but it's the independent variable. The frequency response $Z(f)$ is a function of frequency. The only real parameter is $\beta$, defining the excess bandwidth, but you already know that $0\le \beta\le 1$. You also know that $T_s$ is the symbol period, so $1/T_s$ is indeed the baud rate, which is part of the system's specifications.

From the formula you can see that the minimum bandwidth is half the baud rate (for $\beta=0$, i.e. zero excess bandwidth). For $\beta=1$ (i.e., $100\%$ excess bandwidth), the bandwidth is twice as large, i.e. it equals the baud rate $1/T_s$.