Upward Dog is an excellent position to open your heart.
Some people may suffer from wrist pain when practicing yoga. Wrist pain is often driven from the fact that our bodies are not meant to be put under the extreme intensities often explored unknowingly by participants. This pain is driven from overextending one's wrist past their natural ROM (range-of-motion).
I personally do not have a great deal of flexibility in my wrists. As demonstrated in the video below, I teach you a quick way to baseline your current-state ROM. Once you baseline your wrist-ROM, you can proceed to practicing safely by ensuring that the angle at the wrist doesn't exceed your threshold.
Upward Dog is a great way to increase your natural ROM in the wrists. However, based on your specific body, it may be either impossible or a very lengthly process. Have patience.
Wrist extension is required for advanced positions like Handstand.
Now focusing on the back, the most important part of this posture, you want to try to evenly distribute the extension upon each vertebrae of the spine. If you look at my Upward Dog in the picture above, you'll notice that I have more extension in my lumbar-region/ cervical-region than my thoracic-region. This is what I'm working on now - getting more extension in my thoracic-region.
Lastly this position is key for people that sit on a chair for large portions of their day. Sitting in a chair curves your spine inwards (spinal flexion), so this position helps to reverse damages done from sitting for too long. However this on its own is not sufficient. Back pain must often be treated by evaluating many factors in our life. If you suffer from back pain I recommend you seek a medical professional.
You can practice this position daily - as much as you like - as long as you don't feel any pain. This should be a comfortable position. This position should calm you down. Make sure you're breathing while you do this. I suggest breathing through your nose for 4 seconds on the way in and 4 seconds on the way out. After four breaths, proceed into Downward Dog for another four breaths and repeat.