Key early issue is to understand and model your cash flow. To do so, you'll need to fully understand the timing of yoursales and costs, plus who your key suppliers are, what their payment terms are, and how you can maintain/enhance the relationships. So many small and profitable businesses fuck up because they don't get these basics right. It sounds like a steady business, so should be straightforward.

You'll also need to get started with keeping good financial records. A few spreadsheets will do this if they don't already exist, and it will save you some money with the bookkeeper if you don't want to do this yourself. Don't be that guy that just throws a bunch of invoices at their bookkeeper, who then charges $100+ per hour for data entry.

Finally, never sit back and relax. There's always some bastard looking to steal your customers and offer more/better for cheaper if there are no real barriers to enter your industry.