I am new in practice also and am working towards having a client who also has not previously had a separate business bank account. After some very time-consuming investigatory work, I have found that she takes far more in drawings than she thought she did and her record of expenses leaves a lot to be desiered! Thankfully she is very receptive to advice and is eager to sort out her records once this blasted covid-19 means she can run her business and we can meet up again!
For myself, I don't think I'd want to take on a client who only wants to involve me in one part of the business, because I would find that deeply unsatisfying. Then again, when starting out any client is potentially an attractive client!!
If your letter of engagement clearly states what is in and outside the service you will provide, making it crystal clear that you are only dealing with the cash figures, then I can't see anything wrong with giving him what he is looking for. What he then does with that and any other data is up to him.
Not sure if this is helpful or not but I do sympathise with your position and the newness of all these questions and decisions!