Comments on Tables.
tblCustomers: Not good idea to repeat Captions. Country listed twice. No big deal but it can be confusing later if you are not sure which "Country" you are looking at. Postal Country is different to Delivery Country. Caption doesn't need to be one word only.
tblInventory: Good idea to use double names if possible to avoid using a reserved name. Try ProductCost and ProductTitle.
The reserved name list is very long and there are different versions
Watch out for the Validation (cost) in the table. Maybe just use this in the form.
SuppID combo box should be in the Form, not the table.
tblOrderHeader: Maybe change Status to OrderStatus - Status can be vague.
Move Combo Box to Form.
tblOrderDetail: Remove InvoiceDate - this is in Order Header. Not needed in Order Detail and can cause problems later.
tblPayments: Set Format for Date - maybe short Date?
tblPaymentsMethods: OK but you could just have the options in the Form.
Handy to have a table to make additions but for two options and later, as the database grows, you will be glad it is not cluttered with little tables.
tblStates: suggest change State to StateName. Caption can be State.
Do you want to allow duplicates for ShortState & StateName ?
Table Relationships look good.
Tidy database.
I will study the Queries, Forms and Reports early in the morning. 8pm here now.