I have 3 published books in U.S., seeking foreign publishers, what is best approach?

Hi! I am a newbie to this site. I have 3 published non-fiction books doing well in the U.S. (first one has sold over 45,000 copies). I just convinced my publisher to give me back my foreign rights that they had not yet sold (I audited them and they decided it was better just to give me back my foreign rights then continue to have me pry into their business as it was clear they did not have the resources they say they do to sell titles overseas). So now I'm looking for the easiest and most profitable way to sell my rights to foreign publishers. I've never had an agent before since I found my publisher on my own in 2003 (was actually quite easy). So my questions are this:

1. Would most agents in the U.S. be interested in representing my titles, which are selling well, if they knew only foreign rights were available. (Is it worth my time to pursue this option?)

2. Should I instead just contact foreign agents in the countries I'd like to publish in? If so, can I write to them in English or do I need to write to them in that language?

3. I'm going to be seeking an agent for my upcoming 4th book, if I get a U.S. agent to represent these 3 published book, can I get a different agent for my new book if the one representing the 3 books isn't interested in this? In other words, should I be looking at these books and my new book as two separate issues or trying to put them together as a package to try to obtain an agent?

4. Should I just try to contact foreign publishers myself?

Thanks in advance for your suggestions!

Thanks for your advice!! Appreciate it!