If i get a real estate license in NJ can i sell in other states? Also can I sell in any county in nj?

Your license is restricted to your state unless your state has an association or legal understanding with another state (that's the case where I practice). You can sell anywhere in your state but you might not want to do that as you're unfamiliar with an area outside your comfort zone (ie: your city or metro area) and would be ill advised to guide people on an area you yourself aren't familiar with. So if you have clients going to buy out of your work area or going to sell out of your work area, I suggest using a referral and it's customary to be given 25% of the commission on their end. Also, MLS is generally limited to within your area as many cities in the same state have their own MLS system so you won't have access to it. So it's another reason it's ill advised to help clients in another area as you don't have the information you'd have in your own board.

The NJ license allows you to do business anywhere in NJ. But NJ only. You need a license for each state. However, you can always do a referral to an agent in another state and they pay you a referral fee.

The NJ license allows you to do business anywhere in NJ. But NJ only. You need a license for each state. However, you can always do a referral to an agent in another state and they pay you a referral fee.