If an effect exiles Summon: Esper Maduin and then instructs you to return it to the battlefield, it remains face up in exile (unless that effect instructs you to put it onto the battlefield transformed, in which case it returns as Summon: Esper Maduin)
cards need to be a two-for-one, or better, and thats never more true than it is in Commander, a multiplayer format, where cards are worth a lot less than they are in a 1v1 format
Chances are that casual lifegain Commander decks will just run both of these abilities
Put the rest on the bottom in a random order.) The value of X is calculated only once, as the ability resolves
Either way, this is a 5/5 vehicle for 4 mana with crew 1, so its very easy to attack with, and ramping even one land when attacking is already very efficient