I'd definately recommend getting the rifle in the same caliber I planned for the revolvers. There are many reasons including less confusion at the range/shoot and ease of reloading if you do so and if you don't already after a spell you will.
To answer your second question, yes, a Winchester .357 mag. should have no trouble digesting the .38 special loads.
Congradulations on your soon to be new rifle.
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Gunslinger
We live in a time in which attitudes and deeds once respected as courageous and honorable are now scorned as being antiquated and subversive.