Dear Ali,
FePEST provides not limitation in respect to the number of parameters to calibrate. If you need to include additional parameter (also with different type), you can simply add a new parameter definition (See User Manual FEFLOW 6.2).
There are a plenty of methods for the sensitivity analysis from local sensitivity, where you modify manually the parameters and evaluate the outputs, until complex global sensitivity methods with random realization of parameters. For this second option, please refer to post [color=blue][i]"Null space Monte Carlo with FePest?"[/i][/color] in this forum. Before entering to the sensitivity analysis, you can take advantage of all the FePEST outputs such as correlation matrix, covariance matrix and eigenvalues/eigenvectors in order to have a first idea about the parameter influence on the FEFLOW problem.
Best regards,
Carlos