The tax bill is based on your income, deductions, credits, and tax rates. The amount you withhold or pay in estimated taxes during the year will determine how much you pay in or receive back when you file your tax return (total taxes less amount paid = amount due or refund). How much you pay in via w-2 withholdings vs estimated tax payments can vary, but then end total won't change.
I'm not going to comment on full time employment x2, beyond there's a reason why it doesn't generally end well.
Honestly, given the s-corp and the fact that you have a CPA, they're going to be your best bet. It is tax season, but it's early enough that if you give them all the info ASAP (today/tomorrow), they should be able to at least do a rough estimate for 2020 taxes.