Jessica, you're wise to think about your retirement early in your career. I'm tempted to say that this is especially important because you're not married to your partner (no moral judgment involved, read on ...), but the fact is that the current divorce rate means that married women should think just as carefully about their own finances.
Because you are not married, it's likely that if your partner dies suddenly his assets will go to his blood family, and I assure you that no matter how much they like you, you are likely to end up with little or none of them. Although I'm not big on mindless purchase of life insurance, because you're both so young that it's very cheap, you might consider some term life insurance on each other, to be discontinued after you both have accumulated some assets to cushion the loss of one income.
You indicate that you are risk-averse. You're wise to consider Retirement 2040, but keep in mind that avoiding the need to choose a bunch of funds and allocation percentages doesn't avoid market risk. Retirement 2040 (.PDF link) is currently 90% equities, which is perfectly appropriate for your age. But it means that it will go down and up vigorously. If seeing that on your quarterly statements is going to unsettle you, it may not be the best choice. On the other hand, if having it all in "one package" will make it easier for you to "keep your hands off it", that's a good thing. (BTW, what is your 403(b) invested in, and are you going to change it?)
One reason I ask that question is that you might wish to put the higher-risk/higher-return choices in your Roth, because (with the benfit of time, that is) it would be nice for the highest-returns you get to be the untaxed ones in retirement. Fortunately, while your retirement money is all at the same company (which it may not be 20 years from now if you change employers), your statements from TIAA-CREF will have a grand total and a pie chart that have everything in them at once, to show you where you stand.
I encourage you to look at some online risk and allocation tools, if only to find out what's important to think about. Here are a couple:
(If those links don't paste correctly, I'll come back and fix them.)I have an alternative to the suggestions you've been given here so far. Note, by the way, that if you have the discipline to make (for example) quarterly contributions to your Roth IRA (will your new employer make you eligible for their plan in a year or two?...), you'll not only get investment returns sooner, you'll enjoy the benefits of dollar-cost averaging. I don't think TIAA-CREF has the nice option Vanguard offers, to put $5,000 into a Roth money-market account, and then order 1/12 of it to be invested each month for the next year without further intervention by you. What's great about this is that it almost pleases you to see the market go down (when you're young) because you're getting more shares for your money!)
Because you said you're risk averse, I think you should put 40% of your TIAA-CREF money in TIAA Traditional, 30% into CREF Stock or the Equity Index Mutual Fund, and 30% into TIAA Real Estate. Because you're so young, I'd much rather put less into TIAA Traditional (say,20%), but this very, very, very safe category means that your total will be propped up in times of market declines. I'm suggesting TIAA Real Estate because not only is it a good long-term investment, it's not available anywhere else. It's better than any of the real estate limited partnerships available to your partner (and safer than the direct purchase of that industrial park his sports-car-club buddy is touting) because it's more diversified and cheaper to own. He'll be jealous (just kidding) of your investing acumen. But unlike TIAA Traditional, it can go down during a recession.
There are many other possible answers to your question, just as good as mine. And as your investments grow (and you get older), you'll have to consider the reallocation and gradual adjustments over time.
Tim
