You can try and target more than 6 keywords but it becomes difficult to arrange all that on one page so that real people and search engines can understand it alike.
Repeating keywords within the page excessively is not recommended, it may look like spamming and will not be effective for the ranking.
The numbers should be such that the whole thing looks reasonable and suitable for normal reading. If it doesn't there's a chance, it's overdone.
There are some keyword checkers, sometimes it can be helpful to use those.