Sorry, that's my fault. I saw the word "presentations" thought you were using .Rpres files.
At the moment, I'm unable to find a solution for removing the title slide from the presentation. Css won't help in the instance as the idea is to prevent it from rendering altogether. Removing the title, author, and date arguments will create a blank slide. A solution might be buried in the r markdown presentation docs or in the pandoc user guide.
For increasing the height and width of the slides, use the following css (place at the top of your rmd file). I assumed you wanted the slides to expand to the full height and width of the screen. This css forces the slides to expand to 100vw (width) and 100vh (height). Note: these units allow for the resizing of content relative to the viewport or the content that's currently visible in the browser (alternatively, you can use %). I hard coded the margins to pull the content to the top left corner (the order of the values are top, right, bottom, left). It should work for all screens, but you might have adjust the top and left values. I added border-radius: 0; as the slides had rounded corners.
<style>
body > slides {
padding: 0;
margin: -35px 0 0 -270px;
}
slides > slide{
width: 100vw;
height: 100vh;
border-radius: 0;
}
</style>
EDIT: One more note, the css should be placed after the YAML not at the top the rmd file.