The only thing I'm not sure of is, how do I get the tax deduction? If I set up a payroll deduction, they'll put post-tax money in it. Do I just set it up that way and then get those taxes back at the end of the year when I file? How do other people deal with this question? Are there any other tax considerations I should be aware of?
Some clarification that might be helpful.
Your employer withholds taxes from your paychecks based on your W-4 form that you gave them at some point. This form lets you tell them how many exemptions you have through a small worksheet (states are sometimes calculated differently) and then that allows them to withhold their estimated taxes.
A 401(k) can then be combined with that information to help them estimate your yearly taxes and withhold this from your paycheck. However, tax withholding is an estimate of your actual taxes owed - not actual taxes. When you file taxes, you may get more or owe, depending on how your W-4 was setup.
If you plan on deducting an IRA from 2016, you can actually adjust your W-4 withholding to give your employer the ability to better estimate withholding.
When you create an IRA separate from your company, you tell your provider whether it's a traditional IRA or Roth IRA.