Here is information about making custom menus:
And because there are a lot of misunderstandings and confusions about what a menu is and what to do with the links in a menu, here is a great article for more insight:
You'll want a custom menu on each blog. You are making a chimera so you will have to experiment with the exact top menu items you need. This is an interesting concept, but it might be difficult to pull it off. I believe it can be done, with careful thought.
Some links will have to be sub or child items or your navigation tabs will be too many for readers to easily use. And remember you can link to categories of your posts blog: it doesn't have to be just a "lump" of posts. Though on second thought, the posting blog could act like a blog on lots of websites: almost a separate entity.
I hope this helps. ≥^!^≤ from 1tess to another tess…