xpos and ypos don't work like that. To reposition your buttons, you're going to want to use CSS. The best way, in my opinion, to figure out how to use CSS to reposition your buttons to where you want them to go is by pressing F12 while looking in your browser to pull up the inspector view, then clicking around to find the element you want to reposition, then fiddle with "margins" and "position" until you get something you like. For example.
I'm using the Beta 2.0 version of Monogatari for this, but this method of positioning and styling will work just fine in version 1.4.1, and it's very easy to position things in a what-you-see-is-what-you-get wysiwyg environment like this.
As for your PNG images, this one puzzles me as I have no idea where that white background would be coming from, but if I had to guess it would be either the image itself is being loaded strangely for whatever reason, or that <input type=image> for whatever reason has some strange background CSS affecting it, which you should be able to remove by adding more CSS to set its background color to a fully transparent alpha color. Alternatively, instead of using input type=image, you could keep Monogatari's default buttons and style the buttons to look like images with CSS. I highly recommend using as much CSS as possible when it comes to the positioning, styling, and LOOK of your game, and keeping the raw HTML code for the STRUCTURE of your code.
But again, the PNG white background thing is a MYSTERY to me and I have not seen that happen before. If you figure it out, please follow up and reply to this thread explaining what you ended up doing!
Regarding the music BGM for the title screen, there is an option in option.js to add title screen music. Use that.