So what is your proposed searching intervals for gamma and cost parameters?
Basically, you should do a heuristic grid search by taking some educated guesses at the grid cell sizes, hoping to find a good optimum. Take a look in the Grid.py file in the LIBSVM package. It will give you some hints regarding these values. There are more advanced techniques for doing this, but this is the first thing worth trying.
Second question : What other parameters of LIBSVM do you think i should optimize with my optimization technique?
This depends on the kernel that you choose. Note that gamma doesn't impact all kernel types (like, for example, the linear one). There may be other things that you can try to tweak, but start with these two and see how it goes.