To answer your questions:
1. Yes; from 2018-2025, no unreimbursed employee business expenses are deductible.
2. a. If the lodging does not meet requirements for being at the convenience of the employer, then it should be included in your wages as additional taxable income.
2. b. Correct. These reimbursements do not need to be included. The IRS states in 2020 Publication 15-B Employer's Tax Guide to Fringe Benefits on page 20 for De Minimis Transporation Benefits: You can exclude the value of any de minimis transportation benefit you provide to an employee from the employee's wages.
3. It depends on the rest of the details of your return. How much tax is due will depend on whether you take the standard deduction or itemize, also. To see what to expect, I recommend checking your tax bracket. For 20,000 filing single and taking the standard deduction, if no other income was reported, the tax rate would be 10%.
If necessary, adjust your W-4 now so that 2021 will have enough withheld, see How do I update my 2020 withholdings and print a new W-4?
4. Step 3 for Form W-4 is for reporting dependents. If you do not have a dependent, then entering $2,000 will reduce the amount of taxes withheld through the year. If not enough is withheld, it could result in a balance due when filing your return. It could result in penalties and interest if more than $1,000 is owed.
