You should be fine using unsalted butter. If you think you definitely need salted butter, you could soften it and mix a small amount of salt in with it like you would do if you made the butter yourself.
Sweet butter is another name for unsalted butter. If all you have is salted butter you can just leave out the measurement for the salt.
If you want to make your own butter for a dinner party just get whipping cream and beat it until it turns to butter. Maybe add a pinch of salt. Your choice.
Brown butter is good as a spread, 1/4 cup of butter in a pot and let it melt and foam. It will then settle down as the water evaporates and will foam again. Watch it carefully as it may burn. You just want it to lightly brown and smell nutty. Remove from heat and place pot in a cold bath to stop the cooking. (You just made Ghee also known as clarified butter that is used in Indian cooking) Now you whip regular butter til it's fluffy and then add your "ghee" and refrigerate until you use it. This results in a light nutty smooth butter.