So many great answers and I thank you all for helping out a newbie even though people probably ask this question a lot (thank you for your comment on that, Sol!).
I'm not a great math-accounting mind, so I'm trying to find a simple way I can fit all this in my little pea-brain. My gross income right now is right at about 40,000, but I assume that with the $2,000 I'm contributing to my 401K and the $2,000 I'm putting in my HSA this year, that I will fall below the $36,900 or so starting point for the 25% tax bracket. So I guess my tax rate must be 15%.
And from what you all seem to be saying, you don't want to convert parts of your 401K to your Roth until you're pretty much already FI and have stopped working a real job with huge taxable income, so that when you take the distribution from the 401K, it won't bump you into the next bracket, is that the idea? Otherwise, I guess it would be stupid if I put all my savings pre-tax into the 401K right now while I'm in the 15% bracket and then start converting it when I'm older and probably making enough to be well into the 25% bracket. And I just read somewhere that you can't convert your 401K to anything until you no longer work for that employer...I guess that is another newbie thing I didn't know.
I'm getting the picture now as to what might be a good plan for some folks like me...bulk up your 401K or tIRA as much as you can and put any taxable income you can spare to maxing out the Roth. Then, when you're ready, quit your job and start living off old contributions to Roth and it won't count as taxable income. With little or no taxable income, convert big chunks of 401K yearly to Roth and pay minimal tax. Let newly beefed up Roth grow until 59.5 and continue drawing off contributions as they reach 5 years of age. Is this what a lot of you are talking about? Correct me if I've got it wrong.
Another quick question - I have a small part time job that's only going to make me about $2000 this year. Should I probably see if I can contribute more to my 401K or HSA this year to off-set that so I don't go over the $36,900 mark?
I really appreciate your informed opinions.