Which option is better?
Patreon is a little cheaper and include shipping, but the real value are the other perks. If you are not interested in these, probably the preorder option is quicker and easier. Please note that Patreon include 2 Azure and 1 Caelum (this quantity is not editable).
How many slots are available?
There are around 300 slots available on Patreon (however, there is room only for 33 new Patrons), and only 200 Pantheon Caelum are available via Preorder.
When those decks will be delivered?
My plan is ship preorders and Patreon rewards October 1, 2020