Which android smartphone would you go for if you wanted it to sync its calendar AND contacts with a desktop system directly over a usb cable or encrypted bluetooth link and NOT over the internet? Desktop application will be either Outlook or Zimbra.

That's not how Android works. Android requires Google connectivity to do (almost) everything.
You could try looking for a "new old stock" Symbian, Windows Mobile or Blackberry device which may give you something like what you wish for.

Looks like it can now be done.

http://www.android-sync.com/

i don't know about op's particular requirements; to me it seems they are at least not model specific.
but, as a generalisation this statement:
is not true.
i'm using a stock android phone, have never connected to google with it and do not miss any functionality.
f-droid is my software repository.
i have a calendar.
i haven't looked into it, but i'm pretty sure syncing apps exist.

Which calendar do you have then, and does it sync over usb?

this, itself it just provides a mechanism to use the standard android calendar without a google account.
so any application that would allow me to sync the standard android/google calendar over usb, would also allow me to sync that - i guess. but i've never attmpted it.

fwiw, i was thinking (at some point in the future...) to use some sort of calendar server (CALDAV?) which i can access fro all my devices.
i haven't even researched this yet, but i noticed that there's a few apps in the f-droid repos that seems to be designed for that.

It is time to dump outlook on the desktop side (been running this in a VM since the beginning of virtualization) and find something that:

1. works in ubuntu linux
2. synchronizes with an android app
3. supports calendar, contacts, TASKS, MEMOS just like outlook
4. can synchronize over usb or bluetooth and strictly not send anything over the internet (in fact I intend to rip out the smartphone's antenna to ensure this, this smartphone will be only for offline use)
5. ideally is open-source

You know that you're not the first one to ask this question?
I'm not going to go through your check list one by one, but this:
https://duckduckgo.com/?q=ubuntu+calendar+sync+android
looks like there's quite a few clicks and reads in it.

Thunderbird / (own|next)cloud / davdroid

Although wifi/network connectivity is much easier than usb.

Getting somewhere now, with just open source, and wifi instead of bluetooth:

Evolution on linux +
Syncevolution on linux +
davdroid on android +
wifi router that is only connected to ethernet cable and to SyncEvolution.

Except that, bummer, davdroid does not do memos/notes. What alternatives can do memos/notes? Alternatives to davdroid, or alternatives to everything above?

A fork of davdroid that can do memos, adding a little app to read and search the memos?

very interesting, tell us what you find!

Evolution's notes application is not as easy to search as outlook's.

There is a notes app on android called "owncloud notes" that syncs with owncloud but you access it on a web interface which probably means you need an always-on connection to your home pc. Not very convenient or secure by my standards.

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