What is kept: your username, name, password (scrambled, so nobody can read it), the profile text and photos you add, your posts, comments, +1s and circles, and your notifications. Reports you send are kept for the admins.
Photos: location and camera details are taken out of the photos you upload.
Who sees what: posts shared publicly are visible to every member; posts shared with circles only to the people in those circles. Gplex+ is members-only: nothing is visible to people who aren't signed in. Moderators and admins can see reported content.
Cookies: one cookie keeps you signed in, and one protects the forms. No tracking, analytics or ads, and nothing is shared with or sold to anyone.
Gplex Extended: Gplex+ itself loads nothing from other sites. If you use the Gplex Extended script or add-on, it can show Gplex+ the way Google+ looked in the year you picked; that look may load fonts from Google Fonts (fonts.googleapis.com and fonts.gstatic.com), which then see your IP address, as with any site that uses them.
Your choices: download your data or delete your account in Settings; deleting removes your profile, posts, comments, +1s, circles and photos.
Questions: ziptino9098@icloud.com.