You are correct except for your third bullet point. Grain, which is high is phosphates, causes urinary calculi. Calcium, which alfalfa contains a lot of, prevents urinary calculi.
So, you are good with feeding alfalfa alone. You are good with feeding alfalfa with low quality hay. You are good with feeding alfalfa with a small amount of grain, as the calcium in alfalfa balances the phosphates in grain.
You are NOT good feeding grain with low quality hay.
You want to maintain a balance of 3:1 calcium to phos. ratio.
Alfalfa is 17:1 ratio.
Most hays are approx. 3:1 ratio.
Pasture tends to be about like hay, 3:1
Grain is a 1:5 at best, and 1:7 at worst.
If I wanted to put weight on wethers, I would feed 2 lbs of alfalfa pellets to every lb of grain, to ensure a high calcium ratio. Plus all of the hay they could eat.