That is about it for the content, believe it or not; it is direct and straightforward without any fluff or nonsense. You are simply covering each detail so the seller knows exactly what the buyer intends to do. Having an informal letter of intent also allows for easy negotiations.
Traders are better off NOT using documents like LOI, ICPO, FCO, etc. Even if and when they rarely are used in internal trades, on a restricted level within specific industries, they have no legal or customary basis in International Trade whatsoever. In fact the presence of many of these terms are considered to be signs of Advance Fee Fraud, by knowledgeable players and law enforcement.