The Timezone would be a great choice for your second Lange, especially if you travel. I would agree that a Dato and a representative of the Lange 1 family would be obvious obligatory models for a Lange collection, and next (not necessarily in this order) a Richard Lange, one of the Langematiks ( including Anniversary Limited Edition, Langematik Perpetual, Annual Calendar, etc.), and then perhaps a Zeitwerk.
WIth regard to the Lange 1 Timezone, you might also consider the WG version, my personal favorite:



