EI Transformer design theory questions

[Mephitus]

I have been reading several different books/references about transformer design and theory. So far the hardest part has been with trudging through the math like the horse in The Never Ending Story. But I'm slowly making progress with that. I am wondering about a few design factors in regards to laminated silicon steel E-I transformers that I cant find any specifics on (or may have honestly missed).
1: The dielectric medium that isolates the laminations, how much of an effect does its conductive resistance have?
2: When it comes to windings, what kind of difference is there between primary and secondary being stacked one on the other vs isolated/separate windings? (See attached pic)
3: Alternating each layer orientation |3 to E| vs all layers in the same orientation. What are the practical differences or considerations for this?

[PChi]

1: The dielectric medium that isolates the laminations, how much of an effect does its conductive resistance have?
2: When it comes to windings, what kind of difference is there between primary and secondary being stacked one on the other vs isolated/separate windings?
3: Alternating the layer orientation |? to E| vs all layers in the same orientation. What are the practical differences or considerations for this?
It's

1: At 50 Hz just the scale / finish on the laminations was considered to be adequate to prevent significant eddy currents and this appeared to be the case.
2: The leakage inductance is determined by the flux linkage between the windings with the isolated/separate windings having a higher leakage inductance (probably). At 50 Hz it isn't usually a problem. However if it's 400 Hz then it's time to check.
3: Alternating the E/I s hopefully minimises the air gap in the magnetic circuit so maximises the magnetising inductance so reduces the transformer no load current. Though I guess in practice if they were all the same way round and care was taken to minimise the air gap there may be little difference.

[Zero999]

The configuration shown on the left will have better coupling between the primary and secondary but more capacitance between the windings and it's more difficult to isolate the two coils. It's more common when the secondary is connected to earth anyway so the capacitance is less of a problem.

The diagram on the right, well have slightly poorer coupling but less capacitance and it's easier to isolate the two windings. Quite often the two windings will be wound on separate bobbins. This is commonly used in small mains transformers with no connection to earth on the secondary.