As far as PS Vita UMD backwards compatibility goes. Sony’s UMD Passport program will not be available in the US.
Of course, if you’ve got a Japanese PSN account, you can make it the primary account on your Vita and use Japan’s UMD Passport program. Even then, that will only get you a smattering of the games available on the PSN, and for a price.
If you’ve bought most of your games on the PSN (and not on UMD) you won’t have a problem; the Vita is compatible with downloaded PSP games without issue.