H4 visa for working husband what are the documents needed

Hi,  I have my H1 Visa Extension stamping initiated. 


1. I want to initiate H4 Dependents Visa for my daughter and husband. Can i initiate it now. 

2. My husband is working in QATAR. Please let me know what all documents he needs to get from his company for the visa interview. 


3. My daughter is 3.5 years old. Should i take her along with me. 


Please help me.