Hi, Bryan. I'm not the most savvy person, so take my comments with large
grains of salt. But here's where I would start:
<snip
- Have *manual* calculation saved as the default behaviour for *this
spreadsheet only*.

In the ThisWorkbook module:
Private Sub Workbook_Open()
Application.Calculation = xlCalculationManual
End Sub

- Place a commandbutton (or the most appropriate widget) in the
spreadsheet
itself. The user would click this "Calculate Now" button to perform
manual
calculation of the spreadsheet once all data have been entered or
modified.

In the Sheet module:
Sub Calc
Calculate
End Sub

Assign this to your button.

These specific items are untested, though I've used similar items. Like I
said, I'm not the greatest, but this is where I would start.

HTH
Ed