[Elecraft] K2 Power supply.

[Bill Scovell]

Sorry, I didn't address all of your questions --- here's the rest:-
In a well designed transformer the winding balance should be good and
any small discrepancy between them will not present a problem.
If you parallel the windings you can take double the current rating of
the individual windings.
The field around a toroid is better contained than a conventional
transformer but should still be given due regard,

Bill Scovell / VK2SOE