Technically you are in a "pre-audit" of sorts ... all you can do is wait for them to process the return with the info given ... if they want more they will mail you another letter.
do not wait. supply the information requested, or reply back with an explanation as to why you will not
I run a at home business and all i have is logs of my transactions. Its a cash only business (for now) and a acquired most of the things needed years before i decided to turn it into a way to make money so i do lack receipts to show any purchases that went towards my business but i do however have clients, logged records, and even a social media page showing what products i have and also some pictures showing my work and what i charge. Would these be useful to help me? This is my first year filing self employed, i only made about 13000 last year (i didnt have to reinvest in many materials because of the supply i already had) although this year i will be able to keep more detailed reports as i will be needing to buy many new materials and also plan on selling at flea markets ect.
Send all the info requested or an explanation of what you cannot supply. If you had to prove you had a business to me how could you ? That is the same mentality you need with the state. When it comes to taxes you are guilty until proven innocent and if it isn't in writing it probably didn't happen so do the best you can.