Some cards are needed even if you don't track sales for individual customers, or purchases from individual suppliers
At least one customer card is required to enter invoices, and one card is needed for purchases. If all your sales are to one-time or walk-up customers, you might create a "Cash Customer" card and use it for every sale you make. Likewise, you could create a single "Cash Supplier" card for your purchases.
Employee cards are not required unless you plan to print paycheques for your employees; they are useful for tracking sales by salesperson, however. Personal cards are for your reference only and are not required.