I don't think there can be any definitive answer to your questions; what "looks right" to one viewer of your site could look "overdone" (too many different fonts etc.) to another, with perhaps a third viewer wishing there were an even greater number of fonts in use!
However, the cardinal rule is to ensure you always use only Web-safe fonts, in order to try and ensure that different viewers devices and browsers don't attempt to substitute one font (not installed on the device) for another (that is installed on the device). In the case of devices needing to make a font substitution, the visual effect of your site, which you may well have spent many hours getting "just right", will be lost, effectively.