I don't understand some of your questions but the followings are what I had to learn when I started my ebay listings with Auctiva.
"Preview" button is at the bottom of the each listing. Or at the right side of your saved auctiva listings on the summary page.
Once you uploaded your auctiva listing on ebay, you only can add auctiva template (or changing the pictures) by replacing the entire old contents with the new.
1) Update the auctiva listing by adding or changing the template (or pictures), save it then go back to ebay.
2) Select edit for the ebay item, then click the HTML disply tab. Highlight all (contents) and erase. Now you see the empty box. Do not close this screen yet.
3) Go back to Auctiva and select the HTML link for the same listing item. You'll find the link at the right side of the listing on the summary listing page, right below of "preview" link. You will see the pop-up screen.
4) Click "Select all" and copy-paste back to your ebay listing then save.
It will be easier if you open 2 windows when you do this.