What's more important is thinking about what has to happen. It requires your ears, brain, and body, to all work together, to put the right finger in the right place, consistently. Because you can't be in tune without being consistently in tune. Developing consistency is also what makes it possible to figure out what you're actually doing wrong, and correct it.
I think singing is a good exercise for ear training. There are YouTube recordings of virtually the entire student violin repertoire. Sing along. Get the tune in your head. Also, you can work on this any time, even away from the instrument.
Often overlooked is that intonation is intimately tied to technique because of the consistency factor. There are many schools of technique, but if you just pick one -- typically your teacher's -- and correct yourself when you deviate from it, you will become more consistent, and this will put you in control of playing in tune.
When I'm playing, and notice that I'm out of tune in a particular passage, I analyze what I'm doing wrong with my technique. This is something that never becomes "good enough," but is a lifelong compulsion. They interviewed Ray Brown near the end of his life, and asked why he still needed to practice. He said: "I still need to improve my intonation." That was from a master whose intonation was considered to be impeccable.
Now here's my contrarian view about temperaments. Engineers get worked up about them, but most musicians are ambivalent. Intonation transcends temperament because it has to do with controlling your body and sounding good. Only keyboard and electronic instruments have definite temperaments. String instruments have useful harmonic intervals in some keys (the "fiddle keys") but not others. Wind instruments are all over the place. I don't think there's a meaningful concept of "temperament" in an orchestra or jazz band. But when everybody is in tune, the band has a more powerful sound.
As a final comment: An adult should not expect to make progress at the rate that kids can. And I advise adult beginners to just avoid double stops -- they are not important enough to justify the mental and physical trauma.
