I am not saying you are exactly wrong. It sounds like you are doing the best you know how to do.

I am just trying to help. I have had to figure all this out the hard way (like most people) over 13 years and there is still much I will learn I am sure.
Theoreticaly yes, straight oats and pure alfalfa hay will be just fine along with your replamin plus and free choice salt. That being said, I would add a high protein source (like calf manna or a high protein dairy pellet) to growing kids' oats and to first freshening yearlings' oats. I would do this because these animals are growing still and need the extra protein.
I personaly feed a 16% grain mix to all my girls. I start about 6 weeks before they are due and work them up to about 2 pounds of this mix the day they freshen. After they freshen, I go by body condition to judge if one needs more or less and adjust accordingly, slowly.
My mix that I hand mix is:
10 pounds oats
10 pounds crack corn
6 pounds of Kent ProVider 38 dairy pellet (38% protein)
1/2 pound corn oil
1/2 pound liquid molasses
This mix has worked soooo well for us. We show so we want that extra bloom that it gives. However, if you are just wanting milk and healthy animals straight oats to your milkers with alfalfa is very simple and effective.
My kids get a 20% protein lamb pellet, alfalfa, milk and grow like weeds.