I have the following stylesheets I want to combine:
To combine them do I just paste the codes of the other two style sheets into the stylesheet.css file?
Essentially, yes. If there are any overlapping or conflicting rules, the last one will generally win, so check what selectors are in the various stylesheets and resolve any conflicts first. The stylesheets are loaded in alphabetical order, so you know how they are currently interacting.
Even though fewer stylesheets is a good idea, it might make it more difficult to find some things if you have to search through a 3x-longer main stylesheet. On the other hand, it might be easier to have only one file to search for rules...
I no longer provide installation support on forum for all my modules. However, if there are real bugs with the modules please feel free to contact me
Or if you haven't implemented the developer tools, you search the stylesheet... and the longer the file is, the more lines you have to scroll through to get to them in any case.