the job did tick many important boxes for me?

No, it's not really an idiom, although it is something that most English speakers would understand immediately. To "tick a box" means to select an option on a form one is filling in. This is a figure of speech, and it implies that the speaker has a list of requirements for her employment, and that if these requirements were listed on a form, she would be able to "tick" (mark) many of those requirement which are important to her.

The standard definition of idiom is a phrase, the meaning of which is different than the wods from which it is constructed--for example, raining cats and dogs tells an English speaker that it was raining heavily, but no one believes that cats and dogs were literally falling from the sky. This is metaphorical speech, but the meaning is obvious from the construction.

which, I guess, would make it an idiom.

A form of expression peculier to a language is an idiom, but the language of a people is an idiom as well... It is a sign of nationalism and a rejection of internationalism, or classicism when a people begin writing and communicating in idiom, as I expect Dante did in his inferno and paradiso, and what the Chinese began before Sun Yat Sen... People must first take their language if they will take their liberty... When people are bound in the use of their words to the meaning assigned to them by their ruling class they are slaves because as they speak they think... Control of language is control of destiny...

With that said, check the boxes, that is, on ones list of personal preferences is an example of idiom...

We say "tick" the boxes.

Americans say "check" the boxes.

Americans are silly.

You're really startin' to tick me off, Bubba . . .