Is it possible to get a list of all available players? How do you obtain the Performance Index on each player?

Here.

Not sure what you mean by "Performance Index on each player;" typically the words "Performance Index," to me, refer to anticipated performance or preliminary benchmarks for processes/programs.  That doesn't make sense for a player; a Performance Index might describe the anticipated rate at which games or PAs could be simmed by the sim engine on a new set of servers, but not how well one player might be expected to perform.

There is, however, a Performance History for each player.  You get to that by clicking the words "View Performance History" near the top of the player page that pops up when you click on his name in the draft center.  I don't believe there is a database of all the performance history data; however, I suppose if you wanted to badly enough you could write a program to mine all that data and compile it into a spreadsheet for you.  Never really looked into how Player ID #s are assigned; that would be critical to successfully implementing a data-mining program of this nature.

I thought you were more or less leaving this site flounder from the absurd thread you had sent out before why are you still here anyway flounder.  

The closest thing that I can think of a performance index to select players is the use of advanced stats. Say you are in a $100M league and you want to allocate no more than $12M to your top starting pitcher, who you would like to be somebody like Pedro Martinez. You may want to use parameters like number of innings (e.g. 200 IP minimum), excellent ERA+ (e.g. 250), excellent WHIP+ (e.g.150), and HR allowance of HR/9+ (e.g. 150). You go to draft center and you get Pedro 2000 and Maddux 1995. Take your pick ...  

In the same manner, say you want a modestly priced slugger under $7M for the same league that does not strike out much. You may select parameters like PA (e.g. 650 minimum), AVG# (e.g. over .300), OBP# (e.g, over .400), SLG# (e.g. over .600) and SO/100AB (e.g. under 15). You go to draft center and you get 1996 Gary Sheffield and 1954 Ted Kluszewski. Take your pick ... 

Lol classic!!