During Diwali puja the deity faces South and we face North. Is that right?
No, it is wrong. Seat the deity in the West facing East, and sit so that you look at the deity while your face is towards the North. The Lord's direction is what matters, just as the teacher's direction matters in a classroom.
Related questions
Can a mandir face North or West?
A North-facing mandir is fine; temples of God are often kept North-facing. A West-facing mandir is moderate.
Can a mirror be fitted on a wardrobe in the S, SSW, SW, WSW or West?
No. Wardrobe mirrors also belong on the North or East wall. Some say the North-West is also allowed because the mirror represents the water element and the Moon.
If the mandir on the study table faces East, we would face West. Is that right?
Sit before it so that your own face is towards the North. When you face a consecrated idol all directions become zero; direction is small and the Lord is great.
In my East-facing house the temple had to be on the North wall, so the gods face South; is that wrong?
Do not make the gods face South; it brings heaviness, for example interviews go well but give no result. Place them on the West wall instead so that they face East.
Must the house be at 0 degrees for a sarvatobhadra dwar?
By definition it is at 0 degrees with doors in all four directions, but it can be made otherwise too: build the doors on whichever pads fall on Pushpdant, Grihakshat, Bhallat and E4.
The 5th lord is Mars but the child studies in the West. Is that wrong?
See in which direction the 5th lord sits. If it sits in the West, that is excellent; if in the East, choose the East. The East and North are best for study anyway, and if the lord sits in the South, studying in the South also works.