For 自家食品, should have inventory, need to have inventory records, unless you can proof it the inventory is very small amount and inventory control system.
1. Sales Turnover ($600K x 12) = 7.2 M yearly = (12,000 invoices)
2. A/P --- 500 invoices (500 x 12) = 6000 invoices
3. A/R, even cash sales, all needs records
4. A/P & A/R, how to proof it all is correct and accuracy
5. Need accounting software
6. The freelance needs have an account system, not only Excel
7. The freelance just input data and generate the reports to auditors? need all report? Journal, general ledger, bank reconciliation ......
8. Do you need the freelance work with the audtor? The $4,000 x 12 include this services?
9. The freelance fee, will report to IRD about 56M?
$4,000 monthly (4,000 x 12) is reasonable or not, depends on above matters and the freelance qualification, work performance.