There is plenty of non-seafood dishes to be found without any real preparation, especially in the big cities. That said, if your avoidance of seafood is absolute, then it can be tricky as ingredients from the sea can sneak into a lot of things.

I've never been to Disney in Tokyo so I can't advise specifically on that, but I have to expect that it will be very english and american friendly. It's pretty easy to get by in Tokyo with only english, a little trickier in the rest of the country, but should be manageable.

My biggest advice for first time visitors from America is to plan extra time getting from place to place, and to "relax". I was always used to having my guard way, way up when visiting a foreign country until I first visited Japan. On the first day of my first visit, I met a canadian guy that literally laughed at me for using a pickpocket-resistant wallet.

Have a good time! Learning a little more japanese will get you a long way with the locals...good morning, good afternoon, good evening, excuse me, "go ahead"/"you first", english, I understand, yes, no...It seems like the standing expectation for the behavior of foreigners is so low that a little attempt at politeness impresses.

speaking of politeness, all the rules of etiquette are too much to cover in brief, but if you just pay attention to how your actions are impacting the people around you, and you try to blend in, you'll do well enough.