I think if I were in your shoes I would request the use of the 4 child table and use 2 separate worksheets.  One worksheet considers the 3 children with shared residency, and the other considers the other child.  While I'm not sure the calculator here directly considers this adjustment, one way to fool it into giving your the right calculation is to enter 1 child as Multiple Family Adjustment (MFA) on the shared residency worksheet, and enter 3 children as MFA on the other single child.  You should be able to see from the worksheet that both will use the 4-child table.

That's just me, but maybe there's some other ways to do it.  I think the above plan would be better simply because shared and no parenting time plans use such drastically different approaches to account for parenting time.

No, I don't think we're talking about the same thing.  You wouldn't be putting anything into line C2 under child support paid because that is support paid in a separate order.  This hasn't been ordered yet.  You would get different numbers using the approach I described.  Look into the Multiple Family Adjustment.  The only thing this adjusts is the table used to look up child support.

However, I'm not sure which approach the court would use in such a case.  Every judge does it differently it seems.