Macro to copy items from one sheet to another by vendor and copy to other sheet with running total?

Hello, I would like to make a macro that will copy from 3_Master PO Request, based on Vendor, to 4A_PO Template but only 21 items at a time. I want the catalog #, Name/Description, UOM, and Qty copied over to the form. I have a macro on it that will then export it to the proper file type to allow it to be imported into a premade pdf PO form we have. I would also like anything transferred to 4A_PO TEMPLATE to also be transfered to 4B_2024 Totals but adding it to the next blank line as this sheet will keep a running tally of all purchases in 2024. How would I do this efficiently?