Dynamo and Ivy questions

Follow up from the thread I made the other day about which heroes should I play, I have been playing Dynamo and Ivy the past few days but honestly have no idea/build/gameplan to play them. I have a lot of questions for Dynamo because I played him more than Ivy but any Ivy tips would be appreciated.

1. What is a good build to start learning the hero ?

2. Is Greenamo actually viable or just a shitpost ?

3. Should I play around his Stomp or Heal ?

4. How do I play Ivy ? What is her gameplan/good general build ? Honestly I have no idea how to use her, with Dynamo my gameplan is trying to use 2nd to help my teammates iframe stuffs (like 7's stun for example) and fish for black holes, but I have no idea for Ivy.