To add more photos as you are filling in the week, you just click on "Add photos/videos" or some such again once the first photo has loaded. You can load as many as you want!
If you upload one photo today, for example, and tomorrow you want to upload another photo, click on the "Edit Week" button that's just under the list of weeks (and then a probably obligatory ad)... then go down and click on "Add photo/video" ... you can change anything about that week you want to - you can add more comments, change the nutes, change the conditions, even change the week from veg to flower or vice versa ... you can even delete the week and start over... Once you've done editing the week, it will ask you again to select a cover photo... if you don't want to change the cover photo, you can just hit "cancel" and it will keep the same cover photo.
Good luck! :-D