Type size should always be at least 8pt for legibility. Sizes 8 pt to 12 pt are common for body copy:
When printing reversed text, such as white on rich black or dark colors, with small type below 8-pt, you should add a thin stroke (between .1pt to .25pt) of white (or light color) to compensate to avoid color overlapping and filling the text:
Avoid Font Substitution
Outlining fonts is converting the text into a graphic image. This is done so that your type prints precisely how you have it set. Outlining fonts helps avoid any font substitution (called "defaulting") or rasterized type (pixelated), which will happen if another computer doesn't have your exact fonts. Once you outline your type, the color and size of the text can be modified, but you will not be able to edit the text by typing. You should save a separate layer or file with your original type.
Outlining fonts ensures your typography prints correctly, without the chance of the font defaulting to a substituted one. It also ensures your type prints sharp and crisp on the page, and avoids the need to rasterize type (pixelating it)
Original (Vector) Type vs Rasterized Type
How do I change the font size and font type?