There are not a set number of houses you should see before you decide. Visit as many as it takes to find the one you want. On average, homebuyers see 15 houses before choosing one. Just be sure to communicate often with your real estate agent about everything you're looking for. It will help avoid wasting your time.
Laws vary by state.
Some states require a lawyer to assist in several aspects of the home buying process while other states do not, as long as a qualified real estate professional is involved. Even if your state doesn't require one, you may want to hire a lawyer to help with the complex paperwork and legal contracts. A lawyer can review contracts, make you aware of special considerations, and assist you with the closing process. Your real estate agent may be able to recommend a lawyer. If not, shop around.