@greene, great ideas!
About the writing though, I would stay away from the "short" and "longer" things. These were things that prevented people from posting originally. Same with photos. It took a decent effort to get this forum going and I wouldn't want to discourage members from posting now.
So, instead of "Write a short gardening idea or a longer article to share with NGA folks so they can learn new methods. Photos help to make the idea/article more interesting." Perhaps,
"The Ideas Forum is the place to post your gardening ideas and/or the How To of your ideas. They can be as short as one sentence, or as long as you like. All will be appreciated. Photos are helpful, but not required."
In, "After reading the articles here on the Gardening Ideas Forum, check out the other articles/idea from the recent past (add link here) or the oldies but goodies from the Learning Library (post link here)," I'd leave out the "after reading the articles here on the Gardening Ideas Forum." People can check out those links without reading the IF articles first. Maybe replace that with "You can find additional ideas and articles at (link), and at the Learning Library (link).
HTH.