There are also some general guidelines regarding body vs. heading type sizes as well. Generally 24pt. and above is considered ideal for display sizes, while those below are best for displaying copy. Remember that font size also depends on what dpi your document is set to. It may be obvious but remember that when selecting a font for copy, legibility takes precedence over type design.
Whether you select a sarif or sans-sarif is entirely up to you for the tone and feel you are trying to invoke. That's why in magazines such as the New Yorker, you will find something classic like Garamond or Times for copy. Set spacing is also important when selecting a font size for proper legibility.
I'm not an expert by any means, but those are just a few basics to keep in mind when selecting your font. If you really want to get into the nitty-gritty, I'd totally recommend "Designing With Type" by James Craig: http://www.amazon.com/Designing-Type-5th-Essential-Typography/dp/0823014134