Thanks, yes it's getting closer, I hope, to the solution. I want a private stylesheet which I will store as a template and reuse when needed for new projects of same kind, so ultimately would like to have several private stylesheets stored as templates for various types of projects. I will explore the links you gave and try again hope soon. Have you been able to use Private Style Definitions (PSD) and after selecting some new styles in PSD the new notebook on the right was showing them automatically? As it should following what they say in the Book. Thanks again for help.

I'm not 100% sure I got it but it seems you don't want a private stylesheet but a custom stylesheet shared for many notebooks. Private stylesheet is private to given notebook, it is a part of it. If you want many notebooks to use the same one, then you need to create a new one (can be private too), install it and set it as a stylesheet for desired notebooks. (programmatically via SetOptions+StyleDefinitions, or via menu/options inspector etc).

About stylesheet installation see

http://reference.wolfram.com/language/howto/InstallAStylesheet.html

If you want a custom stylesheet to be used as your default one:

https://mathematica.stackexchange.com/q/132349/5478

Notice that in both those methods the stylesheet is linked so it will not work if you give your calculation notebook to anyone without your stylesheet. You could create a standalone versions by doing SetOptions[calcNb, StyleDefinitions -> Notebook[...]] where Notebook[...] is imported content of your stylesheet.

Am I on a right track?