I only skimmed the replies, so sorry if this was already covered.
I can't easily get alfalfa HAY in this area, so I use the cubes, which I always feed soaked. They are a good way to increase protein in the diet and also, because they are high in calcium, they are easy on the stomach. Sort of like taking Tums with your meals.
The TOTAL protein in the diet of a growing mini is what is important, so you need to "do the math" to figure out what that is. If you are feeding grass hay, which is usually around 10% protein, even if your grain is 14-16% protein, you need to be feeding MORE grain by weight than hay to get the total protein up to 12-14%. That is also where adding alfalfa helps because the protein is higher - more like the grain (best to test your hay). But you also don't want to feed too high a protein level either. That can happen if the horse is getting almost all grain and virtually no hay.
Beet pulp (soaked!) is considered a forage, so that can be substituted for some of the hay. I soak mine for 20 min - 1/2 hour before the PM feeding and keep the rest at room temp overnight for feeding the next morning. It can be an acquired taste, but most of them will get to really like it, even plain (which is what I recommend - without the molasses).