Welcome to the Apple Support Communities. I see that you have some questions and concerns about updating your iPhone 7 plus to iOS 11. I am happy to help address your concerns.
Whether you choose to do updates or not is a personal choice. Here is more information about iOS 11 so you can decide if it's right for you:
iOS 11 - Apple
Any time you do an update on your phone, it's a good idea to do a full backup, either by iCloud or by using iTunes on a computer:
How to back up your iPhone, iPad, and iPod touch
If you do decide to update, the following article has useful information:
Update the iOS on your iPhone, iPad, or iPod touch
Have a fantastic day!