Bastion: Sanctuary: Sanctuary Charm

Sanctuary Charm. After spending a Long Rest in your Bastion, you gain a magical Charm (see “Supernatural Gifts” in chapter 3) that lasts for 7 days or until you use it. The Charm allows you to cast Healing Word once without expending a spell slot. You can’t gain this Charm again while you still have it.

I assume this is cast at first level, but it does not state. Would a warlock cast this at their highest spell slot?

Quote from HawkwinTenebrae >>

I assume this is cast at first level, but it does not state. Would a warlock cast this at their highest spell slot?

This is specified in the SAC.

What level is a spell if you cast it without a spell slot?

Unless the text says otherwise, a spell cast without a spell slot is cast at its lowest possible level, which is the level that appears in its description.

Upcasting for spells specifically says "if a slot of X or higher was used", ergo by definition if you haven't used a slot that part doesn't come into play unless there's specific verbiage that says otherwise.

Would a sanctuary or a similar special facility made by a cleric count for them as "dedicated to their deity" for the Word of Recall spell?

I'd say so; the limit basically just exists so it can only go to particular points instead of letting them drop a safe landing point at wherever is most convenient at any given point in the adventure/campaign.