When you have a Pages document, you can always go to File -> Save as Template
After you’ve saved it, whenever you chose New -> From Template Chooser, you have a small section that says “My Templates”:
Your “Custom” templates should appear there.
For the second part of your question, what you need is what Pages call a section. The steps for creating a new section are pretty straightforward and you can find a lot of information on google, see samples here and here (find the part where a new section is created).
In short: Insert a “Section Break”, edit it, change the styles, add what you want (see the links to see tips about different things you can do, like having a different ‘first page’ than the rest, etc.).
Once you’re happy with your “section”, make sure the ‘caret’ (cursor) is blinking in any part of the section and go to Format -> Advanced -> Capture Pages:
The result is a sheet dialog like this:
Give it a name, make sure it includes the pages you want (1, 2, 3 or all, depending upon the complexity of your idea, in your case it would be ‘First Page Only’) and finally save the document as a “Template”.
The page(s) you’ve used to create a Section can be safety deleted before you save the template (unless you want your template to always start with those pages by default), because you have captured them as a section, they will always be available under the new template.