If you plan at some point to go back with her yes start now and yes you have to register your marriage in the consulate here .
As she does not have a green card she can not get a SSN but she can get a Tax payer ID number ( you have to love the IRS )
For you tax liability it would not make a difference as you do not spend enough time in the US and have no property . But at the time you want to get her a US passport or a green card the first thing you have to provide is tax records so having her in the filing papers will save you a lot of aggravation later on .
As for the Roth IRA Really not sure sorry.
