I have a small travel theme site. It ranks SERP first page to last place. I have only 3 pages and competitors have hundreds of pages. Would it be significant benefits to increase the number of pages in the site? And if so, what would be the easy way to create a large number of pages, for example related to travel destinations, schedules or weather?
If you have something in mind to create new pages about, go for it. More pages gives more opportunities to rank for different keywords and bring in more traffic. If you're happy with where you're at now and don't feel like you need to grow, then stay put and keep up your hard work. If you feel like growth could be good for you, go for it!
To be honest, you could optimise and build links for your few pages to rank. At the end of the day though, the sites you are competing with will have more authority, more information and probably more traffic (from all of the pages). Content is King (as they say) and Google likes large websites...
No any benefit to add supplemental indexed pages to the site. Only main indexed pages will ordered to increase traffic to your site. Use this Supplemental Index Ratio Tool to check the Supplemental Index Ratio for your site.
SERP doesn't depend on the number of pages, it depends upon the optimization. If you have 3 or 100 pages, use unique title & meta tags for it. then it will be more helpful in increasing SERP for your site.