How can I construct a Band-pass filter from a low and a high-pass filter? Suppose, I need to construct a Band-pass filter in OpenCV. But, I know, there are no functions in OpenCV for Band-pass filters. 

Now, what I need to do is to have a low-pass filter and a high-pass filter and combine them as a series. That is, first, the image would be passed through a low-pass filter and then the output of that low-pass filter would be passed to a high-pass filter.

Am I correct?

Now, what kind of low and high pass filters should I use? Would they be,


Gassian low/high pass filters
Mean low/high pass filters
Median low/high pass filters
Sobel filters
or, anything else...
Yes you are correct. You apply them if series in they are linear.

One simple band-pass filter you could use is called the difference of Gaussian (DoG)

The procedure is: 


Create a Gaussian filter with a small variance
Create a Gaussian filter with a large variance
Subtract the latter from the former to create a band-pass filter
Apply the filter to the image


There are a lot of different filters to choose from depending on the application. A good paper is "On the choice of band-pass quadrature filters" by Boukerroui, Noble and Brady. It has an analysis of the DoG filter as well.