While this is only a personal project for fun, please keep in mind that some countries, such as Germany, have strict laws about personal data. And even if they do not have those, as the developer you are always responsible for your code and the data you gather. Face recognition is a mighty and scary tool, so maybe you can use it to teach your guests in a fun way about it?

Also, many face recognition systems are based on open source datasets that are NOT balanced. This can lead to your non-white, non-male friends being not recognized ect. This is both a real problem and also to a dampened mood at your party. Have fun, but be safe and conscious about it!