Hey yo Haps,
may I ask ya a question? Why the off number for points, you could simplify things so much with the basic number of players minus player rank plus one formula (otherwise known as n-r+1) which is soooooo close to what you wanna do and will work whether you have 10, 9, or 20 people right off the hop, no fiddlin around.
To answer your question, yes you can do it, and say the word and I will write it out for ya, just seems kinda like a lot of typing for very little when you consider the above suggested formula.
As for your second part question the answer is yes, it is possible. Open up the Stats tab, click on the Filter button and in the new window on the bottom right hand side click on the Overall Scoring button. Now I'm not all that keen on this part of the program as I have never really dabbled with it, but looking at the help file, I think this would be what you would want to put in the window for a formula. If I were you, I would wait for a second opinion before going ahead with it though:
assign("c", count(scores))
average(top(c-3, scores))