Can 现在 go first? 现在我们要去海关?
Yes, that can work also.
海 (hǎi) = ocean/sea/great number (of people or things) as in Shanghai (上海)
关 (guān) = mountain pass/to close/to turn off
海关 (hǎiguān) = customs (i.e. border crossing inspection)
Can this be also translated as: ＂我们现在必须要去海关＂？
I think we cannot use both 必须 and 要 at the same time, it's one or the other.