Hi Mona, welcome on these forums!
To have similar media links open in different sizes, you can do the following:
1. On Settings > Media activate the option to include the jQuery Metadata extension
2. Then go back to the page where your media links are and add size data to the link class like this example:
<a href="//ulr.of/my.mp4" class="button fancybox-iframe {width:480,height:360}">watch my movie</a>
Autoplay is not possible unless supported as a GET parameter by the browser like for example href=”//ulr.of/my.mp4?autoplay=true” but I’d be surprised if at all widely supported…