The juice in the crushed pineapple should be just enough to wet the mixture, but you don’t want too much extra juice.
Pineapple tidbits are a great size to add a little bit of texture to the casserole. You can also use pineapple chunks, which are typically much larger. I would recommend cutting the chunks into a bit smaller pieces.
If the center of your casserole is not heated and melty after 30 minutes, you can cover with aluminum foil and continue cooking so that the crackers on top of the casserole do not get too dark brown.
I always recommend grating your own cheese from the block when it comes to baking. Prebagged shredded cheese contains anti-caking agents which prevent the cheese from melting as well and can sometimes cause the texture to be grainy or chalky.
Store leftovers in an air-tight container kept in the refrigerator for up to 3 days. Reheat in the microwave or covered with aluminum foil in a 350F oven.
For Making Ahead of Time - You can prepare the pineapple filling, cover it with plastic wrap, and store it in the refrigerator a day in advance. You can also prepare the Ritz cracker topping minus the butter, and store it separately from the pineapple filling in a ziptop bag kept in the refrigerator. Assemble your pineapple casserole the day of and bake as normal.