Form 4852 - Calculating Line 7 Withholding without Pay Stub, Calculating Line 8 (Form 1099-R) as well

I never received my W-2 from my employer. His reason for not sending it is that his payroll company (Heartland Payroll) never gave him the W-2s because of his personal debt to them.    I waited the ascribed amount of time and never received it. I then called the IRS and received the FORM 4852 but I have no pay stubs and I am locked out of my account on Heartland Payroll.

Fast forward a few weeks: I managed to work out the amount of gross income by taking the hours worked on my “timekeeping receipts” and multiplying them by my hourly wage. However I have no idea how to calculate my withholding (recently tried the IRS withholding calculator but it is asking for suspected future wages for 2020?).

I do not have any pensions, IRAs etc so the total amount for line 8 would be $0 correct?

What is my next step? Thanks for the help!