Hmmm I keep getting various questions from Americans about this. I should probably sit down and write an article on this.

Anyway to answer your questions. Yes knowing German helps a lot. Strongly related languages. Helped my American wife a lot.

You can be a bit strategic about part of Norwegian/Swedish you learn. It may not be obvious to you what is most useful to learn now. But a lot of learners material get into stuff like "Hi, how are you doing?" or examples of "Where can I find the buss stop?" That kind of stuff is a waste. You can just ask that in English.

The value in knowing the language is really in being able to read signs and labels, because you cannot ask a sign to switch to English.

Learn e.g. what different cuts of meat is called in Norwegian/Swedish. Because that can be confusing when you are in the groccery store and try to buy meat but have no clue what the labels mean.

Words related to employment. When looking for a job online, a lot of it is in Norwegian. You can often find English ads, but the user interface will have a lot of Norwegian buttons.

Words related to banking is also useful as not all internet banks have English translations. Know what checkings, savings account is called. Bill, payment, withdraw, deposit etc.

Also government related stuff. A lot is translated to English, but not always. Words for tax return.