you can remove that week, if you want. it's up to you if it is worth the effort.
yes, you can still add weeks after you add a harvest week. I just did so with my Vanilla Creme Pie diary. I posted a harvest yesterday, but the 2nd plant is taking longer. I could have also just saved the pictures of first harvest and waited until the 2nd plant finishes...
there's some benefit to holding off and doing it together later on... there's a time limit on the rating you select, so if you somehow change your mind later, you can't change the rating. Could alwys delete and re-do the harvest or week, too. So, no big deal either way...Keep the images stored locally, or download them before deleting the week. Can even copy/paste any of your write-up to easiyl recreate the week with minimal effort.
do what is most convenient for you.... lots of ways to skin this cat.