Contractor 2 week notice

I have been a contractor for a consultancy company for 8 yrs. I am now converting into Full time employee. When should I tell my employer(consultancy company) that I am leaving them and becoming a full time employee with other company. Should I tell them before 2 weeks ? or less than 2 weeks.

What type of benefits should I ask from them so it will help me with my future immigration/employment situations.

This depends on your employment terms however in most cases it is hire and fire term in the US so technically you can leave the day you resign however most people give at least a week of notice to the H1B employer. You dont need to tell what employer you are joining.

This is again subject to the employment agreement.