Well try just

{ "keys": [".", "."], "command": "insert_snippet", "args": {"contents": "->"} }

and ensure you have a comma between every {"keys"...} section.

This seems like something you could accomplish by writing an ST2 plugin, which either performs AppleScript evaluation itself, or just watches some local file for commands or Python statements to be placed in it; and then write something on the AppleScript side to populate that file.

Probably the easiest way would be to add something like this to your user keybinds file:

{ "keys": [".", "."], "command": "insert_snippet", "args": {"contents": "->"}, "context": [ { "key": "selector", "operator": "equal", "operand": "source.php" } ] }

Having not used Textmate/Chocolat, I'm not sure what you mean. 

Does shift+rightdrag perform the effect you're after?

If so, you could copy your Packages/Default/Default (OSX).sublime-mousemap into a new Packages/User/Default (OSX).sublime-mousemap file, then change the bindings to the way you like them. 

Though AFAIK there is no way to persistently toggle between selection-modes, you just have to use the correct modifier key/mouse button to use column selection mode.