Input alias having a place holder which gets selected when the alias is used

Please try:

SetOptions[EvaluationNotebook[], 
 InputAliases -> {
   "aa" -> RowBox[{"AFunctionWithAVeryLongName", "[", "\[SelectionPlaceholder]", "]"}]
 }
]

A placeholder with a name does not seem possible with Input Aliases.

You can create a placeholder with a name if you use a TemplateBox:

CurrentValue[EvaluationNotebook[], {InputAliases,"aa"}] = RowBox[{
    "AFunctionWithAVeryLongName",
    "[",
    TemplateBox[{},"SelectionPlaceholder",DisplayFunction->(FrameBox["\"input\""]&)],
    "]"
}];

Then, using the alias "aa" produces:

which can be selected by tabbing. Alas, the placeholder is still not selected when you use the alias.