Hi Roz! Welcome to the Forum!
I'm not sure of the intricacies of the Kindle Previewer - it's been awhile since I used it. Hopefully someone else with more experience there can jump in. However setting up a "cover" and a "title" page I can help with.
If you go into the menu bar in Sigil and select "Tools/Add Cover" it will open a popup and allow you to select which image you'd like to use then click OK. That's it! Sigil will create a page (or update one if it is already there).
Creating a Title page is just like any other chapter in the book. Right click on a file in your "Book Browser" window and select "Add Blank HTML File". Then use HTML and CSS to style it however you want. Something along the lines of:
Code:
<h1>Title</h1>
<p class="series">Series<br />
Book Num</p>
<p class="auth">Author</p>
with CSS:
.auth, .series, .subtit {text-align:center; text-indent:0; margin:0; font-weight:bold; font-size:1.1em}
.subtit {margin:1em 2em; font-size:.8em}
.series {margin-bottom:1em}
.auth {margin-top:1em; font-size:1.4em}
I keep the two pages separate from each other, but you mentioned you wanted them combined. You can do that by wrapping your image with SVG tags, but that is a more involved process. The easier method is to use your image editor of choice (photoshop, powerpoint, etc.) Add your Title and Author, then save that as a new image which you would use as the cover image as above.
I hope that helps some!