I very much recommend the Toyota Commemorative Museum in Nagoya itself, but not so much for the car stuff as for the huge warehouse of FASCINATING weaving machine technology (which is where Mr. Toyoda actually got his start!) Make sure to go at a time that lines up with taking a tour, because they will demo a lot of the machines!!! I also recommend the factory tour (along with the Toyota Kaikan Musem) in Toyota city itself for car stuff. It's a big time investment to get there though, and you MUST sign up in advance. The museum by itself is not worth the time without the factory tour.

4-5 hours

夏休みでなければそんなに混雑しないと思います。 ただ会社の勉強会、観光バスの団体などもある可能性あり、 どこの観光地もそうですが、「早め」の時間が空いていると思います。　見学時間はさらっと周るか、じっくり見るかで違いますが、私は昼過ぎから夕方（13時半頃～16時半頃）までで説明をじっくり聞き、車もゆっくり見ました。 説明してくれる人の知識や、説明への熱さが感じられ、とてものめり込めたので、じっくり見学をお勧めします。

Take the yellow hop on hop off bus from one of the few major attractions in Nagoya, it will take you there right at their doorstep

Around 4 subway stations. It’s near Sake station, then around 10-15 mins walk.

Not sure if they have anyone who speaks Portuguese. However, this seems likely due to a fairly large Brazilian population in Nagoya.

Photos are welcome. The in house guides were very friendly and knowledgeable. Entrance is very affordable at ¥500 per adult. Do Google for their website for more information.

You can take Meitetsu line to Sako station. It is one stop north of Nagoya station. From Sako, you'll need to walk one block in south direction.

As far as I know, there is no "Mitsubishi Garden Hotel Nagoya Premier". Guess you are making mistake about the name. I think it must be "Mitsui Garden Hotel Nagoya Premier". If so, the distance is less than 2 km and so possible to go with walk and not too much expensive by using a taxi.

This is about 2.5 hours from Tokyo by train "Shinkansen"