When planning your site, it's important to limit the amount of your content because it all needs to load at one time. Four to six separate content areas or "pages" seem to be about the norm for many single-page sites.
The amount of content in each section should be sufficient to fill a maximized browser window running at high resolution. You may want to consider the visible area your visitors likely see within their browser. Crafting your sections to fit comfortably within that space can minimize scrolling while viewing individual sections. Keep in mind that the smooth scroll is designed to scroll the page up so that the target heading is at the top of the window, which means that your last section should have sufficient content to allow it to scroll all the way to the top. If that's not possible, all you need to do is to assign the last section a large amount of padding on the bottom. Don't worry about small screen users having to scroll within sections. Remember, we are not hiding the browser's scroll bars—they are still usable, as are mouse wheels and arrow keys.