So here's the deal. Whether or not you have to even report any assets depends on two things:
#1. your income for the FAFSA year (note, this is not current year income - the current FAFSA for the 2017-2018 tax year actually uses 2015 income information) - If you earn below a certain threshold (<$50k) AND
#2. you filed a 1040A or 1040EZ tax return
then you would qualify for the simplified method. If you qualify, you literally don't report any asset info on the FAFSA itself (whether or not your school will still require your asset info is school dependent)
Assuming you don't qualify for the simplified method, FAFSA does not actually include any retirement accounts as part of your assets. So if you put your money into a retirement account, that money will not be counted toward your EFC. **However, do note that if you are contributing to an IRA or 401k that lowers the income you're reporting on your tax return, FAFSA will add that back when calculating your income. It can be confusing because while the assets themselves won't count, if you get a tax benefit in making the contribution, that will count as income.
The whole thing is rather confusing and it took me a while to completely wrap my head around it. The best source of information is here:
https://studentaid.ed.gov/sa/sites/default/files/2017-18-efc-formula.pdf
You'll want to look at the 5th and 23rd pages - these were the two pages I found most relevant.
I think you should aim to get your FAFSA EFC as low as legitimately possible because you never know what type of aid money you can get depending on your EFC criteria. At one school I interviewed at, they mentioned that all students with an EFC less than a certain amount would get a guaranteed grant each year of I think $8k. So it's definitely worth your while to learn about will/won't count for your EFC and whether or not you think you would qualify for any aid that uses your EFC as the main criteria.
Last caveat - you might not want to tie up all your assets by putting them in retirement. You can still leave some as an emergency fund and not have it add too much to your EFC. You can google EFC calculators and play around with the numbers and you'll see what I mean.