You do not need to set up everything on day one. Pick the one job that would help most this week, do it for real, and let the next job follow.
A job is a small, real piece of work. Sending an invoice. Taking a booking. Selling a product online. If you finish it, you have something that works.
1. Choose the job
Look at what costs you the most time or money right now. That is your first job. It might be chasing payments, keeping track of appointments, or taking orders from your own website.
2. Set up only what it needs
A service invoice does not need a full product list. A short description and a price are enough.
An online shop does need clear products, honest prices and a checkout that works on a phone. Do those, and leave the rest for later.
3. Do it for real, once
Run one real customer through the whole job. Send the invoice and watch it get paid. Take the booking and turn up for it.
One finished job teaches you more than an afternoon of settings.
4. Add the next job when it is clear
Once the first job runs, the next one is usually obvious. Maybe it is stock, or a second person on your team, or messages to customers.
Add it then. Your customers, sales and payments stay on the same record, so nothing has to be typed twice.