Unfortunately, I can't tell you an exact number that is the "right" number of keywords on a page, mostly because that's the wrong way to think about keyword optimization.
There's no keyword density you should be aiming for -- in fact, using a keyword too many times can result in penalization due to "keyword stuffing." Just keep the reader in mind, and only use keywords when you need to. You'll find enough natural opportunities to include keywords that you won't even have to worry about reaching an arbitrary number.