I might be able to help here too. My trip to Japan was last fall spending three weeks in the country dedicated almost entirely to amusement parks. I did 4.5 days at Disney, 4 days at USJ, 2 days at Fuji Q, 2 days at Nagashima Spa Land and a day at a few other parks: Tobu Zoo, Joypolis, Yomiuriland, Hirakata Park, etc.
I don't speak any Japanese but didn't really have any trouble with language at any of the parks I went to. Most (90%+) of the park workers at all of the parks I went to knew enough English to have a basic conversation of "where's the bathroom" or "I want to order that one". The other 10% you'll be more than fine with pantomiming or Google Translate. I almost entirely stuck to Tokyo, Nagoya and Osaka but the normal comment is that English knowledge gets worse the further you get from the big cities so YMMV.
I found transportation to be so simple in Japan. Google Maps has all of the train and bus routes available on the app and was probably the #1 reason I was able to have a successful trip. Make sure you have a data plan and Google Maps and you'll be shocked by how easy it is like I was! As far as Fuji Q goes in particular, I originally planned on a train up to Fuji. It's supposed to be super beautiful but the night before on a whim I decided to see if I needed to buy tickets. Turns out I needed to buy them months in advance and I didn't realize it. So last minute I went on Klook and booked a bus fare to Fuji. It boarded from Shinjuku Station where I was staying, had plenty of room for my luggage and was overall really simple. I took the early one and was at the park with plenty of time for me to check into the hotel and drop off my luggage before the park opened for the day. If you're able, I wholeheartedly recommend the Highland Resort and Spa. With the weak yen, it wasn't much more money than a standard Hilton or Marriot in the States and was one of the nicest hotels I've stayed at anywhere. I also had a great view of the park from my room and was able to watch the fireworks while laying in bed (I would've had amazing pictures if the whole window didn't fog up!) But if you don't want to stay, I think a bus round trip in a day would be totally possible and common.
As I'm sure you know, Fuji Queue has a reputation. I didn't think it was quite as bad as some people say but I had early entry through my hotel and was pretty liberal with buying skip the line passes. Eejainaika is as crazy as people say or maybe even crazier but if you're a SoCal person, you know what you're getting yourself into. Fujiyama was a big surprise for me, super smooth and fun with some great airtime.
I adore Japan and am planning on going back this year, hopefully to knock out a couple more parks that I wasn't able to do last year like Shima Spain, Greenland, Nasu Highland as well as revisit USJ for HHN. I know you'll have a great time!