You can select on the FAFSA that you are interested to be considered for federal work study, you might not be awarded it, and you will have to find a job. You are not required to use the work study if you don’t want it, you can decline it later.
Income and tax information from 2017 is used. Asset information is of the day you submit FAFSA.
If your parents filed 2017 taxes married jointly, then you can use the IRS data retrieval tool in FAFSA to import the tax info. Then you only have to enter the parent 1 and 2 income from working by hand because on the tax return it was added together. Tax form and exemptions and such will be imported by the retrieval tool.
If you didn’t file taxes in 2017 the school might need a non filing verification from the IRS for you. And if you don’t use the data retrieval tool, you might need a tax transcript for your parents.
The 401k contributions your parents made in 2017 are not on the tax return, but they are listed on their W2 in box 12. There is a question on the FAFSA asking about it among other questions about untaxed income.