Just revising while the clock it ticking :D, I want to make sure that I fully grasp the two above concepts.
Forwards: These are contracts made between two parties over the counter, and accordingly exchange of money has to take place at initiation. The long may pay the short if the initial price is higher than the contract value or vice versa.
At the termination date of the contract, not the termination date of the underlying asset, if there is a difference between the contract value and the market value this determines whether the contract holder benefitted or not, but no money exchange takes place at this point.
Futures: these are contracts made between two parties but not costumized, it is based on the contracts available in the market. There is no payment taking place in the beginning but it is marked to market every interval of time.
An exchange of money may occur at initiation (if the agreed price of the underlying is too high or too low), but it is by no means a certainty.
I’m not sure what you mean by the initial price.
The long will pay the short if the agreed price of the underlying is less than the arbitrage-free price; the short will pay the long if the agreed price of the underlying is more than the arbitrage-free price.
The futures contract is an agreement for the short to sell and the long to buy the underlying asset at an agreed price on the termination date. Of course money will be exchanged: the long will pay the short the agreed price, and the short will deliver the underlying asset to the long.
. . . one of those parties being the clearinghouse of the exchange on which the futures contract is traded . . .
. . . but the counterparty to the clearinghouse is required to post a margin . . .