Any expense tracking app that allows 1) customizable categories AND subcategories; 2) mappable spending to more than one "accounts" 3) different currencies 4) downloadable CSV or XLS reports?

Try Money Manager from RealByte. ALL of your points are covered in that app, and much more customizations are available. They have their app-using-only a separate blog, where you should have a look to and find more deep configurations that will automatize your wishes, as for me, in the best way. Greatest functionality.

Hi, I use Toshl Finance. It can do everything here except different currencies (which I'm not sure because I only use SGD). For the multiple accounts tagging, I'm not entirely sure what you mean by that, but you can split a single spend into multiple transactions with different taggings.

What I like about it is that you can use it on your computer as well as your phone, although do note that the bank transaction syncing can only be done via your phone, and the computer will subsequently synced to whatever is on your phone. (Meaning main device is your phone, computer/web version is just easier to use to edit stuff)

You can give it a trial run to see if it works for you before deciding to continue the premium subscription. Full transparency, I'm using premium because I forgot to cancel before the trial ended, but I find the app still rather decent.