я с удовольствием принимаю ваше предложение о работе, но хотел сообщить,что для меня удобнее было бы начать работу в сентябре
I am delighted to accept your job offer. However, I would like to inform you that I would prefer to start in September.
it's my pleasure to accept your request but i must warn you it would be more comfortable for me to start working in September
количества знаков не хватает чтобы сделать должный перевод с приличествующей лексикой
Александр, "предложение о работе" is "a job offer", not "a request" and "but I must warn you" is not something a normal person would write or tell to the employer. I mean you can do it if you have no intention to actually work for the company 😄
Also "it's my pleasure to accept..." sounds extremely odd in such context.