How to Design a Scalable Database Architecture for Automotive Garage Software?

I've started building automotive garage software, but I'm facing some challenges with its database structure and how to connect different features. I want the software to keep customer details, vehicle records, repair orders, estimates, invoices, and parts information organized in one place. What is the best way to connect all this information so shop owners and staff can easily find what they need?

I've also explored some existing products, such as Torque360, Tekmetric, and Shop Boss, which offer similar solutions for automotive repair shops. I'm planning to build a similar product and want to understand what features and functions I should consider while developing my own software.
I'd also like the software to help repair shops manage daily work, such as tracking ongoing repairs, checking parts availability, and keeping customer records updated. For developers who have built similar systems, what database structure and features would you recommend to make the software useful, reliable, and easy to expand in the future?