I see only two categories. One is net wages and salaries, and the other category is transfer payments. Transfer payments include taxes, rents, royalties, interest and dividends. Part one falls into the first category, and the other two into the second. Whether a payment is to one's own workforce or to a supplier - including his workforce, is irrelevant.
Every sale is also purchase, so the amount available for both is equal.
But at the commencement of trade there is an absence of purchasing power, and so credit is created to prime the pump. One cannot start a game of Monopoly until the players have been given money by the bank. Real life is the same. An expansion of an economy also requires new credit. It is credit which initially makes it possible for the whole of the productive capacity of the community to be absorbed.