What deliverables should I expect from a programmer for our business?

Forgive me if I use the wrong terms.

My family has two businesses: a quarry and a villa. My father wants to create an ERP (quite like Oracle and Netsuite) for both businesses and will hire a programmer(?) that he knows. He wants it specially made because he wants to keep the data within himself and to fully customize it to our needs (quarry is a medium-sized business while the villa is a small-sized business, and our employees are mostly tech-illiterate since we are in a small town in an ASEAN country.)

Since this is a big investment, what advice do you have in getting this done?

Specifically, what deliverables should I expect from the programmer? Much like when commissioning a graphics artist for a brand kit, they provide the logo, brand colors, etc., what's the programmer version for this?

Furthermore, what kind of NAS would be good for this purpose if anyone knows? I'm planning on buying a Synology for our family's personal use, but we're also intending on using the same NAS for the business. Is that advisable?

Thank you so much for anyone who answers.