I see. So each player simply gets 5 points for buying in. That is a small change to the formula. The (5 * buyins) part just becomes 5.
5 + (5 * numberOfHits) + (switch(rank, 1, 33, 2, 22, 3, 12, 4, 8, 5, 7, 6, 6, 7, 5, 8, 4, 9, 3) * (10 * buyins))
You could use the Points for buy-in and Points for hit fields, but those are usually meant as easy ways to award points if you don't want to use a formula. The TD will award points for any of those fields, including the Points for Playing field, that you put a value in. Thus, if your Points for Playing formula includes points for knocking players out and you also fill in the Points for hit field, you'll be awarding double points for knocking out other players.
It has been my experience that you should use either the simple fields or the Points for Playing formula field, but not both. It tends to end up being a source of frustration when trying to figure out why your points formula isn't awarding the points you think it should be.
So, the above formula should be good. It includes points for buying in, points for knocking players out, and points from the points prize pool.
Oh, oops, I forgot the decimal point on the percentages.
5 + (5 * numberOfHits) + (switch(rank, 1, .33, 2, .22, 3, .12, 4, .8, 5, .7, 6, .6, 7, .5, 8, .4, 9, .3) * (10 * buyins))