Savings don't count as income, so you will need something (side-hustle income, dividends/cap gains, unemployment, etc.) to get you above 138% of the Federal Poverty Level (maybe 100% of FPL in some states?) before you qualify for ACA. Below that, you qualify for Medicaid or other low-income forms of healthcare.
Showing a pay stub -even an old one - won't affect whether, at the end of the year, you were eligible for the premium tax credit (PTC). Only your tax return determines that. So, if you think you will be over 138% FPL for the year, show the pay stub, and if you can't get the PTC now, at least know you'll be able to get it as a refund when you do your taxes. But I think you could be in for some issues if you go on ACA, and then can't show income above 138% FPL at the end of the year.