Hello, I am a solicitor with over 20 years experience. I will try to answer this.
I can be sufficient - you do not necessarily need to draw up a documents formally headed "contract" to make a contract. However, an exchange of letters must be rpecise and accurate and clear and make it clear what the terms of the agreement is. If there is any doubt/lackof cl;arity then htis cna led to disoutes later on. YOU might be better off getting a lawyer to draft a formal agreement for you.
Your spelling mistakes and poor use of the English language, ie 'what the terms of the agreement are not is' causes me to question your answer.