How fun! There must be tons of the language still kicking around your head. Why not just go full speed on WK? At some point when the reviews come around, if it was all easy now, it will be easy later. As soon as the lessons cover challenging/new content, taper it down a bit at that time.
But if all the kanji and vocab on WK level 10-11 (where you’d get to before your trip) still looks too easy, another option is to get a book like Kodansha Kanji Learner’s course (similar concept with mnemonics and vocab), and just read through it quickly up to the point where you need to start actually studying. But you have to manage it yourself, so despite being more flexible to speed ahead, it can be slower if you don’t actually do it.
you know I think instead of a structured grammar approach, if what you want anyway is to interact with people, perhaps listen to a lot of YouTube videos in Japanese. There is content for every level and real life situation imaginable. Perhaps go through the recommendations linked in this thread and videos people post to find the right level for you. If a lot just comes back to you, you might not have to study but rather just make use of videos directed at people learning Japanese to get things refreshed.
Other things people do that would relate to your goals - lessons with a tutor on italki.
Another way to make grammar relatable and with audio would be to subscribe to Satori and go through their grammar series and some of the stories (there are grammar glosses underlined in the text). They also have travel related series. And it integrates with WK