Store cards that can be used elsewhere always count (i.e. Best Buy Visa) but YMMV on store cards that can only be used at a particular retailer (i.e. Kohl's). AU cards, business cards that report on your personal credit report, and closed cards also count. Your scores and existing credit lines should be fine for a CSR approval. As for other travel cards, there are many ways to get to Japan. Alaskan and Delta would be two that immediately come to mind.
All revolvers count.
Unless you travel a ton, the Amex Plat isn’t worth the fee. Maybe the first year but you have to actively work to get the return. Is it worth $500 a year to you? I said no and went gold. Maybe later platinum will make sense but for most it doesn’t. That fee eats away any extras you get with any other card. Keep that in mind.
Chase Sapphire is the better deal. All the Chase cards are. Again, keep the fees in check. I got the Bonvoy for my “travel” card. I have my 3 other Chase cards for points and such.
From experience, Chase relies heavy on Experian.