Preserving fish with acidified rice is still done, albeit it's not so popular these days. In Kyoto, sushi rice is generally a good deal more acidic than you're likely used to, because in the West we always get Tokyo-style sushi (the dish we eat was invented in Tokyo), and it does indeed preserve slightly: the fish is slightly "cooked" in the same way that ceviche is slightly "cooked" by the acid.
Yes, sushi rice always has seasoning, but the precise ingredients and proportions are somewhat contested (and in some cases held secret by this or that sushi chef -- those guys get oddly worked up about thing like this).
The big trick for those outside Japan to learn about making sushi of all kinds is that 99% of the art lies in the rice. If you get that right, the rest is fabulously simple (unless you're shooting for high-end perfection, which is a whole 'nother thing): you just slap stuff on rice, and roll it if you like. But the rice is complicated and tedious and time-consuming.
Basically the deal is that you make steamed rice with some combination of ingredients (like your list: mirin, vinegar, sugar, etc.). Then you toss it in a drying bowl (usually wooden) while fanning it. This polishes the rice, and dries it a bit, yet keeps the interior of each grain moist. Then these grains can be manipulated by hand without simply squashing them, and they can be formed into things like nigiri (rice balls).
I leave the details to people who want to debate them.