Like any good lawyer answer: it depends.
In Texas or Michigan, if you have a single parcel of real estate, our minimum recommendations are 1 LLC but a 2-company structure provides more protection.
In Texas, if you have multiple parcels of real estate, you likely need one series LLC at the minimum but a 2-company struture provides more protection.
In Michigan, if you have multiple parcels of real estate, you need at minimum one LLC per parcel of real estate, with possibly a holding (parent) company and an operations company.
If you have accumulated enough capital that you are able to purchase assets in cash, it may also make sense to create a "financing" entity that will act as a bank would, and lend money to your holding company in exchange for a lien/mortgage on your property.