Hello and welcome to the RTA forums !

The first thing that should be of concern to you, is your means of transport. It is very dificult to rent a car under the age of 21 years in the US, and even then it becomes very expensive due to young driver fees that are added daily to cost of rental.

It is even more difficult to purchase a car as a visitor to the USA. So I will start with the question, have you arranged transport and overcome the difficulties associated with it as an 18 year old ? If not, I think that is something you need to look into before getting deep into your planning.