天门阵:Skygate fort/camp?
majestically: gallantly?
金鼓:金 is not gold, it's a different kind of instrument,like 鸣金收兵
番王:sort like "chieftain", at that time, those tribes from north were looked down as barbarians. It would be appropriate to look into the literature on the invasions of Huns and Goths to the Roman Empire to find a good word.