How to enable single-clicking to launch files & apps?

1) As far as I know, no, that's not possible.

2) Cmd+ click.

 

Have you tried putting your applications in stacks on the dock? It would still be two clicks to launch but not a double-click.

 

I found Quicksilver today, new mac user for three days, greatest thing since sliced bread. spotlite is quick to, cmd + space three letters of app then enter.

 

Try Alfred its basically the same thing but better . They also have a power pack extra but adds more features but the basic version is free