Gideon with Mobile Tactician and Masterstroke - I'm assuming he gets 2mp for both commands, for a total of 4 movement points?

Does this count as getting movement points during a special action, since command is a special action? Must he spend the 2 movement points immediately, or can he save them? Is it the same deal that if he uses the movement points, he loses the trigger "after resolving command" and can't do the second command from Masterstroke?

The movement points received from Mobile Tactician are not received as part of a special action. Mobile Tactician is not a special action. Receiving movement points during a special action is not the same thing as as part of.

Gideon gets 2mp twice during Command + Masterstroke-Command. Movement points received from Mobile Tactician go to his movement point pool. He cannot spend movement points between resolving Command and exhausting Masterstroke, because spending movement points has a different trigger and he would miss the trigger of Masterstroke.