sonjay - 10:10 pm on Dec 20, 2012 (gmt 0)
The .psd won't determine any of those things. The HTML & CSS that are used to create the WP template will determine those things.
If you have specific requirements (i.e., a 3-column option, variable-size slider, etc.), make sure those are in the specs so that whoever creates the html & css knows to allow for those options.
But .... the visual design of the .psd can make it easy, hard, or impossible to offer those options in the html & css, so make sure your designer knows your requirements too, so that he can design a visual look that can be adjusted to accommodate those requirements.