I have the field already added and part of the site. That was the easy part (see attachement). I also know that the data is stored at $ userinfo[field5], so I could query that field to make sure it's not null.
Unfortunately, like you, I don't know php that well, so I don't know how to proceed.

Also, I'm not familiar enough with templates to know what templates to add and how to make them work properly.