The first employee changes the books more than any new customer. You register as an employer with Revenue, report pay in real time on each pay date, and start recording wages, employer PRSI and the amounts owed to Revenue. Most startups use a payroll product or bureau for this and post the totals to their accounting software.
Set up the payroll accounts in the ledger before the first pay run, not after. Getting the structure right once avoids a messy correction across several months.
Once a startup has investors, a monthly or quarterly board pack becomes routine. If the books are reconciled weekly and closed monthly, the pack is an export plus a page of commentary. If they are not, it becomes a week of work every time. The habit pays for itself the first time a board member asks a detailed question about spend.