DS nearly 8 received Mindstorms for Christmas - he has asked for it for 3 years and we finally believed he had the computer and reading skills to really do it on his own.
We were right - he started playing with it immediately and was able to do some basic programming. The building aspect is not at all challenging for him - he can build massive lego kits in no time - the programming is harder - but he is learning and the software is pretty intuitive (he has spent a bit of time learning Scratch and that helped).
So far for storage we have just used the box it came in which has been fine - but a plastic tub would be more sturdy. There are not that many pieces (chuckle - compared to all the other lego pieces floating around this house) so while a divided tub would be handy - I wouldn't say it is necessary. We have a few technic kits and I can already see my DS considering poaching pieces for what he wants to build.
He also received "The Mayan Adventure" and because we had to travel after Christmas that came in handy since he couldn't take Mindstorms - instead he read the book portions that make up the story (there is a story thread, and then a building and programming thread). Now he is re-reading the building and programming thread and we are going to start working through the projects. I like this because I think it can be hard to come up with "what do I do with this cool new thing I just got."
So far, the only problem I can see with Mindstorms is that 1)I have to give him more computer time and 2) he seems far less interested in the many other Lego (mostly Star Wars) sets he received from family for Christmas

Cat