Everything I have read about and seen on mobile designs usually have a screen width set to a maximum width of 480px. Also, usually a line or block height for links is around 40px to allow for, dare I say, fat fingers on a touch screen. As for fonts, I follow the rule of thumb that sans-serif fonts are better on screen while serif fonts are better for print. I also keep font sizes at defaults setting them at 1em or nothing at all. And tags like <h> can have a weird effect. Not all mobile devices support CSS well and even if you set your tags to a specific font size, it may be ignored.
I would still discourage you using an automatic redirection. However, when I need to use a script for mobile devices, I use .asp as most of my sites run on .asp. When possible, scripts are better server side.