Just finished deity Japan dominance victory. It's totally doable just like with England. The Japan island can hold 2 cities. You should settle your capital on the silk and at the same time you will also find Seoul. So that means +1 culture and +2 science from the start, not bad! Religion was a bad option to go for, won't happen, went for harbours first instead. After that I build a campus to the capital and a commercial hub to the second city. The double adjacency bonuses from districts is awesome, I was getting +6 gold from well placed commercial hubs and +4 from harbours! I struggled a bit to get the first Admiral cause there were 2 other civs going for it. I missed the second one, don't know what happened, it was 100 points away from the closest civ getting it and suddenly it was gone. Someone bought it with faith or gold I guess. But that doesn't really matter cause you are getting +5 strength from shallow waters anyways.
The biggest problem I had was that there were no China, India or Australia. I had to take on Hong Kong and Seoul. Gilgamesh was the closest one to me and he had a city in the middle east. I needed to chill and wait for about 10 turns for frigates before I went for Kongo, then Germany who had the whole Europe for himself and I also build another fleet to take on Gilgamesh who had now settled Asia. I got battleships after I took their first cities so it was a breeze to Uruk, Aachen, Cairo, Tenochtitlan, Rio de Janeiro and Nidaros.
The one major thing that is different from playing England this way was that with Victoria, you could settle on any spec of never heard dirt you find and build the half cost harbour with very little production coming, but with the full price harbour on Japan you need to atleast have a couple of good production tiles where you settle.
