However, within the last couple of months I have switched jobs and got married, the combination of which has raised my/our combined MAGI to above the maximum allowed for Roth IRA contributions.
Are you going to be above the MAGI limit for the year overall? Marriage is considered as if your status on Dec 31st were your status the whole year. However for the wage income, your job and salary don't matter, what matters is the total income of you and your spouse for the tax year. Also your income is counted after the 401(k) is deducted. So it's possible you might not be above the limit.
- Do I have to switch the whole balance of my Roth IRA to a traditional IRA, or can I just recharacterize the 2011 contributions (so I would still have a Roth IRA containing my 2009 and 2010 contributions, I just wouldn’t contribute to it any more)
I'm sure you don't have to recharacterize the whole account, just the ineligible contributions. I fairly sure I've read that there is a way to calculate how much of the account must be recharacterized, based on investment earnings since the contribution was made.
You might also be able to resolve the situation by withdrawing the excessive contributions.
I am surprised the brokerage couldn't be more helpful. Perhaps you should call back and ask to be transferred to someone who has experience with the process.
- When I eventually retire and withdraw money from my traditional IRA, am I going to have to pay tax on the whole lot? Or just the earnings?
Just the earnings. Good luck keeping track of that for a few decades!
- On a slightly different note - I’ve read it’s desirable to have a mix of pre-tax and after-tax retirement contributions, and I already max out my 401k at work. Now that I’m ineligible to contribute to a Roth IRA, what other investment vehicles should I consider for after-tax retirement contributions? Should I just keep contributing $5k a year to my new traditional IRA, or are there better options out there?
Yes, definitely desirable. There is a way you can still contribute to your Roth IRA though, regardless of your income. What you have to do is contribute to a non-deductible traditional IRA (which as far as I know, anyone can do regardless of income). And then, convert the account to a Roth IRA, which you can do regardless of income (since 2010). You have to pay tax on any earnings but you can minimize that easily enough by converting the account quickly and investing in a money market fund temporarily.
The biggest wrinkle is that your conversion has to come proportionally from all traditional IRAs. So if you have a tax-deferred traditional IRA, it gets more complicated.