When I was at that length I did the following.
Protected my ends like a JEALOUS LOVER!!!!!!!!!!!!!!!!!!!
A Lion protecting her lion cubs!!!!!!!!
I did my best not to lose length if I could. So I did almost everything you have there I never showed my ends during this time. I knew that my necklaces, clothing, scarves around my shoulders, coats, EVERYTHING was out to get my ends and take them off.
I sleep in head wraps of some sort, baggyed, twists and braids, deep conditioned, cowashes, low to no manipulation. At shoulder length is when I went 365 days without using any heat with the exception of heating caps or hair dryers for deep conditioning. I also did wigs and 3/4 wigs to protect my ends also, that required some type of cap around my hair so that the wig did not rub up against my hair.
I started a hair journal which is now almost 400 pages long. I read and researched everything I could get my hands on. I visited fotkis like crazy and folks that would let me get copies of pictures of their length I would put up around me and place in my journal.
When my hair was in twists or braids I would make sure to moisturize or spritz my hair every single day even if it was with glycerine and water. Something moist was and is in my head every day. You really get the benefits of this when you take your hair down. For me it was easier to remove the twists and braids. Hair did not have the snap, crackle and pop sound (all you naturals understand this sound all too well!)
Find products and a routine for you and stick with it. Remember the ends are the laziest, and weakest part of the hair so you have to treat it like the high maintenance princess it is.
Truly, no joke.
Now truth be told, I am still doing the protecting because if I lose my ends I lose my length. The longer my hair gets the OLDER my ends are, when you learn this for gaining length at your shoulders it will be this way from now on if you want to maintain length.
I have cut down on some of the other routines, such as baggying and I don't deep condition twice a week like I use to, but those ends.....I don't play. They are forever under my watchful eyes and treated like a HMP (high maintenance princess.
You have some very sound advice given to you about this. I hope that all the ladies who are now at shoulder length take heed and can use some of the advice give here. It is very valuable and produces positive results.
Happy growing.