Calculating the core area for a low frequency transformer part 2
I know the saturation point of the core material


Core saturation has nothing to do with secondary current or even the extra current drawn by the primary when the secondary is supplying current to a load. This is because the H fields generated in the core from load currents in primary and secondary totally cancel each other. It doesn't sound intuitive but it's the truth that matters!

Core saturation is to do with the small current that flows into the primary when the secondary is, in effect, removed.

So you don't need to switch the formula because whatever you do, and under whatever load conditions, the flux in the core remains the same for no-load and fully loaded conditions.

In fact, due to leakage inductance and copper losses, the core flux reduces on higher secondary load currents.


  How does the turns ratio of 8:1 influence the values for the Induced
  Voltage and the Number of Turns that I need to put in to the above
  formula? 


It doesn't affect core saturation


  At first I thought I should just use the primary coil values,
  then I thought I should add the primary and secondary together. 


It's just the primary (driven winding) that produces flux and hopefully, that should be clear by now.