Keep in mind, in this article
https://blog.peoplevine.com/blog/30637, you can replace almost ANY page with HAPI if you want to retain our standard URL paths.
To hide the account nav, start by identifying in your code.
Notice the ID account-nav, we can use that to hide it by adding this css to your layout.
#account-nav {
display: none;
}
As you can see it's now hidden.
Now, you can add a new set of HTML to the layout that is set for logged in members.