When can I file my 2017 tax returns?

I am doing freelancing for two different companies and I have several questions. I deliver for them digital files, such as research, PowerPoints or excel files. Do I need to add sales tax to the invoices? When and how do I file taxes? I have never worked before in California and just started working in October last year.

If I participate in my employer's 401K plan, can I also set up a SEP-IRA for my self-employment income?

What is a Future Delphi credit scoring and how does it work?

Can I claim child tax credit for my son born on December 31?

How many people actually go in for a Health Insurance? It is observed that most people think it is a waste of money so avoid it. What do you think?

What is the best way to become a financial advisor?

What are the some available defenses against product liability claims?