I can’t see how the features table will link to the users. I would consider either putting the feature fields into the users table so their values are stored along with the rest of the user data or add a field in the features table which stores the user id. Make sure it’s unique so you don’t have more than one record per user.
You can either update everything when the form is submitted or put actions on the checkboxes to update as they are clicked. The first way is easiest but the second way might give a better user experience.
Hope that helps.
EDIT: Is the uid_fk field the link to the users table? If so, you should be good to go with the second option I gave.