You can target as many as you'd like, but it would be wiser to focus on just one main keyword and a couple secondary keywords.
It's really your call as to how many keywords you want to use. The important thing is to think about your capacity to rank those keywords. Going for 2 keywords per page would be good, according to me.
On home page, you can target 2 to 3 keywords, this would be perfect, if you use too many keywords then it would marked as keyword stuffing which is not good.
Keep this in mind, Google ranks pages, not entire websites. So if you were to have a handful of keywords, just have each page dedicated to only about 2-3 keywords. That way, you don't spread yourself thin.