Type styles
Your website should use a type style that reflects the nature of your business.
However at the moment there are restrictions on the styles you should use.  No matter how you format a web document it is rendered by the browser on a remote PC that will not have all the same fonts as your computer.  Web documents that are formatted in fancy fonts can easily be unreadable.   The standard offers a range of 'generic' type styles that will be rendered reasonably accurately on most platforms: serif, sans-serif, mono-space, cursive, and fantasy.  
Here are some examples.  Note that although the styles are different the sizes are all set the same.  The width and the readability vary quite a lot!
Generic Typical Atypical
Serif Here is some text in Times Roman Here is some text in Gloucester MT Extra Condensed
Sans-serif Here is some text in Arial Here is  Gill Sans Ultra Bold
Mono-space Here is some text in Courier Here is text in OCR A extended
Cursive Here is some text in Monotype Corsiva Here is some Old English Text MT
Fantasy Here is some text in Westminster Here is some text in Curlz MT
This is what the section above looks like on my PC

This is what the section of type above looks like on my PC

Type size is also an issue - a compromise between readability and page content.
There are many ways of specifying text size. Different browsers respond in different ways to these, not all recognizing all the alternatives. Don't forget the browser can be set to use larger or smaller sizes at the user's choice!
Starting from the basic (unmodified) font sizes your browser uses, there are HTML font sizes <font size="1"> up to <font size = "7">
CSS adds xx-small, x-small, small, medium, large, x-large, xx-large, as well as points, picas, pixels, exs, ems, inches and cm/mm.   
Description Advantage Problem
Point size Predictable when printed out rendered differently between platforms - e.g. larger on PC than Mac.
Pixel size predictable on-screen size supports layout with graphics prints tiny on laser printers
Percentage lets user keep control of print sizes - helpful for visually impaired very unpredictable layouts
CSS lets user keep control of print sizes - helpful for visually impaired limited range & very unpredictable layouts
em precise and flexible browsers don't support it properly

 

Pixels per em is a crucial concept. As much as any other single factor (such as x-height), it determines the legibility of characters on screen at a nominal point size. The higher the ppem, the better defined are the characters' features, and the more and larger decrements are possible before hitting the legibility floor. If the ppem of the base size is low, fewer and smaller steps are possible.

Pixels-per-em refers to the number of screen pixels required to render the 'm' of a font at a size given in points.

A point is 1/72". On a system displaying 72 pixels per logical inch (Mac OS standard ppi), 1 point equals 1 pixel. On a system displaying 96 or 120 ppi (standard Windows settings), 1 point equals 1.333 or 1.667 pixels, respectively. The formula for points per em (ppem) is a(b/72), where a is the font size, and b is the logical resolution figure.

For example, 12 points at 72 ppi (the legacy Mac OS browser default) or 9 points at 96ppi have a ppem value of 12. Twelve points at 96ppi (the legacy Windows browser default), or 16 points at 72ppi both have a ppem of 16. Twelve points at 90ppi have 15ppem, and 12 points at 120 ppi (Windows "large fonts") have 20ppem.