Ask HN: Which step comes first when forming a startup?

Tomorrow, we're getting our first investment. As soon as we receive this investment, we're going to use the money firstly for the lawyer, to form contracts and agreements between the founders and to form our corporation. The investment is coming from a private party, so my question is do you need to have a lawyer involved before-hand, or is it ok to consult one after you receive the investment. (Investment is 100k)