iPhoto Library

Before using iCloud Photo Library, I would back up all my photo and videos through iPhoto on my Mac Air and through an external hard drive. It was easy because I would back up all my photos to my EHD and then delete my photos I didn't want on my phone knowing they were still on my EHD.

When I switched to putting everything in iCloud Photo Library and paying for extra storage in the cloud, I can't figure out how to back up my iPhoto library to my external hard drive.

How do you still back up everything so if I delete something from my iPhone, it's still saved on my external hard drive?

Also, I though that using iCloud Photo Library would free up more space on my phone. But I'm still using 25+GB in my photo storage. Am I doing anything wrong?

Thank you for your help!