What is your process like for doing data science projects?

Whenever I am starting a data science project I tend to get overwhelmed when it is time to scale data, insert it into a model, etc.

1. Do you struggle to find data or clean it up?

2. Do you guys find yourselves having to add more data over time?

3. Do you work step by step with the model? I.e you slowly add columns to the data?

4. And lastly: Do you guys fully "understand" things like K-means, scalars, etc.? I use them in models, but struggle to fully comprehend them beyond their basic purpose.