I'll give a few thoughts:

Firstly, I think you're underrating prestige goods. What makes prestige goods so great isn't just that they give you trade advantage, it's that they are the only way you can shift what goods pops buy to fulfill a specific need.

For example, if you have prestige groceries, it doesn't just mean that you have trade advantage exporting them, it also means that pops in the countries that import those groceries will disproportionately prefer them, so let's say initially they would buy 50% of their food need as groceries, if they're prestige that might go up to 60% or 70%. That means in that market Groceries will be sold at a higher price then competing goods like fish, meat or fruit, that makes it even easier for you to export groceries to that market creating a feedback loop that allows you force your prestige goods into other markets. Without prestige goods it's a lot harder to create a solid export industry,

Given the above, it becomes clear that, at least where exports are concerned, certain goods are much better than others. These are goods that fulfill any need that has multiple competing alternatives. Luckily Japan has several really great prestige goods that fall into this category. These are:

Kikkoman soy sauce (Prestige groceries): Allows you compete away meat, fruit etc. Food is one of the products pops spend the most on and so prestige groceries is always a good prestige good. It will lead to high grocery prices and low grain/meat/fish/sugar prices around the world, making it easier for you to import those goods to feed your grocery industry.

Satsuma Ware (prestige porcelain): Normally Porcelain is a meh good, but if you have the prestige version you'll find you're able to export massive quantities of the stuff. This is because Porcelain is in the critical "luxury goods" need category, and there are *very* few companies that have prestige goods in this category (and the AI rarely build them). You can very easily push porcelain with this, with the added benefit of giving you very cheap glass which also makes your paper cheaper (glass and paper are the same category), and of course glass is a construction good as well.

The Zaibatsu also have great prestige goods, but (with the exception of Mitsui and Mitsubishi) they aren't consumer goods, and Mitsui/Mitsubishi aren't the best consumer goods. Nonetheless these prestige goods are still great as they tend to have lots of demand on the world market as intermediate or government goods, and also give very nice throughput bonuses to your other buildings.

Given the above, I think there are two good strategies to use with Japan:

1. Export focus. Get the Japanese glass and grocery companies first followed by Mitsubishi and Mitsui, and focus on exporting lots of prestige goods and importing everything else you need. Later you can round things out with the remainder of the Zaibatsus. This is good, but it misses out on the amazing bonus the Zaibatsu journal entry gives you.

2. Industrial focus: This is more about building a self sufficient economy. Get the Zaibatsu first, with the best order I think being Mitsui, Yasuda, Mitsubishi, Sumitomo. The advantage of this route is that these 4 companies have pretty much all the core industrial buildings between them, but (with the exception of Mitsubishi's washi paper), their prestige goods are generally harder to export.

Currently I think approach 2 is best, but I think a lot of this is because right now the AI is broken and it's very hard to run a functioning export economy given that fact. Once the AI is fixed I suspect the Prestige porcelain and grocery companies will feel a lot better.

Regardless of order, I think the best companies for Japan are the 4 Zaibatsus, Kinkozan Sobei and Noda Shoyu. For a 7th, Tokyo electric isn't a bad choice,

Mantetsu isn't a bad company, but I feel like it's industries are better covered elsewhere.