I will answer you by deconstructing your post #1 on the thread that you linked to.
In the retail forex market, there is no buying or selling of currencies or currency pairs.
In your scenario, you did not buy anything. You speculated (placed a bet) on the direction that the EUR/USD pair would move. You bet that the pair would increase in value – that’s what it means to go LONG.
A currency pair is simply a mathematical ratio. It has no physical existence. You can’t hold a currency pair in your hand; you can’t deposit a currency pair into your bank account; and you can’t buy or sell a currency pair. But, you can bet on where its price will go. That’s what we do in this market. We bet LONG on pairs we think will go up. And we bet SHORT on pairs we think will go down.
The short answer to your question is:
For two equal and opposite trades – one LONG and one SHORT – in the same pair, at the same entry price, with the same position size, the required margin will be the same.
Note: This answer does not apply to simultaneous LONG and SHORT positions. This answer does not describe a hedging situation.
Correct.
However – being a stickler for terminology – I would say that the notional amount of the trade is 10,000 units of EUR/USD.
Refer to my comments above regarding buying and selling (which does not exist in retail forex trading).
Yes, as described above.