Sushi started as a way of preserving fish for a few days, this the vinegar. If you don't use vinegared and sweetened rice, it's not technically sushi.
The flavor of sushi rice varies a great deal regionally and by preparation. For instance, Kansai (Kyoto/Osaka) you tend to get sourer rice than Kantō (Tokyo), but sushi is also a lot less common in Kansai. In Kyoto you're more likely to get sliced fish with plain rice on the side (sashimi, or in Kyoto otsukuri).
Fish may be plain, lightly salted, lightly pickled, torched, seared, etc. Seasoning on nigirizushi and makizushi may include wasabi (usually fake) or not. Dips for sashimi may be ponzu, soy, Tosa joyu (dashi-enhanced soy, aged), etc.
So do what you like and don't worry.
As to sake and mirin: it is not difficult to get acceptable if mediocre sake, e.g., Gekkeikan. It keeps well so get a big bottle. Real mirin can be much more difficult. If the ingredients list is more than 3 items, it's almost certainly fake. Use sake and add sugar as a substitute: fake mirin is like that "cooking wine" you see in the grocery store salad dressing aisle--disgusting.