I added spiderable package to my app.
When I load my pages with ?_escaped_fragment_= it renders my page correctly, like it is a static one. But when I try to render it with 'Fetch as Google bot' using Webmaster tools and ask for a version without this query parameter, Google shows a blank page with some basic meteor scripts included. Not sure if it's the expected behavior or an issue with my setup.
That is expected behavior.
Use tools such as Screaming Frog Seo Spider to check if your Ajax Crawling Protocol is ok.