My boy has moved out, and as much as I'll miss him, his room is now mine!

Well... He's still got some stuff to sort/clear out and still pops in every so often, but his old room is slowly getting cleared while I plan what I want to do in there. Definitely blue walls for a start.

What I would like is a desk made from the Ikea expedit/Kallax(?sp) 4 cubed at the ends (77cm x 77cm) but wondered about the sizes in regard to the Really Useful Boxes. Would this be a good working height once the bench top is screwed on?

I have several 7Lt and 35Lt RUBs and was wondering if these fit into/onto the shelves or would I need to get something different? As much as I want it all done now, I don't want to make any expensive mistakes either.
Thank you for any help
Jo x