That sounds like a quality diet - Rice bran is a fantastic weight picker-upper. Be very Careful with it though! Very often our ricebran come moldy or even once we got it with TONS of moths in the bucket!! They must have harvested/processed it while the moths were cocooned and they all came out by the time we got it! What a nasty surprise.
The BEST joint supplement I've ever found has been MSM, if she has bad joints already MSM with Glucosamine is the best option.
MSM is: MSM contains sulfur in a form the body can readily use. Sulfur is necessary for the production of collagen, glucosamine, and chondroitin, all of which are building blocks of cartilage. Sulfur is necessary for the formation of all connective tissue in the horse's body, including cartilage in joints. Sulfur also works with thiamine, pantothenic acid, and biotin to promote metabolism and communication between nerve cells. Sulfur is found abundantly in keratin, a major component of hair, hooves, and skin, and it's included in some horse skin, coat and hoof supplements. Sulfur is also necessary in the formation of glutathione, which functions as one of the body's best natural antioxidants.
My mare has a serious reaction to bugs, and gets ripples on her belly where the collagen has deteriorated from twitching and rubbing so much. When I started her on MSM this got Immediately better! Most horses these issues will cause permanent ripples in their skin, hers are gone completely.
As for Brewer's Yeast: It isn't for joints or anything, it simply makes it easier for them to process their feed. Here's a good link that explains it best: http://www.admani.com/horse/Equine%2...th%20Yeast.htm
Also for horses with ulcers (Of Course! Speak to you Vet!!) but I find Magnesium helps a great deal. Here's a fantastic link about Magnesium. This is an all-to-forgotten supplement that horses Need. Magnesium- The Mineral Superhero
Looks like you've got a good understanding of it all :)