There are many restrictions that apply to an ESTA visa that you need to be aware of.
Firstly, the visa does not guarantee entry into the United States and you may still be denied entry at the discretion of a border official.
The ESTA visa does not make provision for working in the U.S. If you need to work, you must apply for the appropriate visa and meet with the necessary criteria for working in the States whether on a part or full time basis.
You also cannot study on an ESTA visa USA and will need a student visa if you wish to study in the country. You will need to fulfill the eligibility criteria for applying for a student visa.
Family members cannot travel on the same ESTA visa however application can be made as a group especially where minor children are concerned.
An ESTA visa is valid for a period of 2 years after which application will need to be made again. If the visa expires while you are in the States, you should reapply immediately. Applications are processed relatively quickly and you only need to apply if you plan to visit the U.S. again and your existing Visa has expired. It is however recommended to make application as soon as possible before traveling. The visa is active from the date of approval and not the date of travel.
The visa allows for a maximum stay of up to 90 days. Should you need to extend your stay beyond this, you will need to apply for a different visa. You will need to leave the country after the 90 day period and can only return after an equal period spent outside of the United State. For example, if you visited for a period of 60 days, you will only be allowed to return after spending 60 days out of the country.