What We Did to Save the Kingdom might be a good title for a fantasy novel for grown-ups.
Yes, go with it.
Not really, sorry.
I would be pretty neutral on it and would have to look at the cover art, read reviews, etc.
I recuse myself from answering this question as I do not read fantasy novels for grown-ups or have opinions on their titles or for some other sound reason known to me.
Also, if you ran across a book called What We Did to Save the Kingdom, what, if any, preconceptions would you have about it? (Funny, serious, high fantasy, swashbuckling, sword-wielding protagonist, lots of boats, whatever.)