Rd13,
Please ask all the questions you want!
1. It's like Pacoenes said. GPS stands for "Got it, Played it, Sent it"
2. You are right, there is no "trade in progress" but the offer is there once you send the proposal. And it does not remove the resources from your availability so if you are not careful you might offer the same resource to two different nations!
3. It's not in the houserules but there is an implicit agreement of "no reload" in Multiplayer games.
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