What to feed a horse?

I have done lots of research on horse feed but I do not know what would be best to feed when I get my horse. I'll be getting a horse soon there isn't one that I have in mind and would most likely adopt but I just need some overall tips. I was thinking sugar beet pulp was a good concentrate I could feed and then Timothy hay. I know it depends on the amount of work your horse does to determine what type of food to feed like with alfalfa that is high in protein. I would only ride my horse about 3-4 times a week nothing too tiring. So I just need some help determining what combination of feed would be good for an average horse working at an average amount or so. Again I was thinking of sugar beet pulp and Timothy hay. Also I need to know how much to feed.