Script for selecting layers / files from the drop-down menu.

I'm not sure what you mean by previous specified folder. Is that the folder where the current active document is located?

Here's a script for listing the layers:

#target photoshop
var doc = activeDocument;
    var layerList = [];
    var idxList = [];
    var layerSets = 0
    try{doc.backgroundLayer}
    catch(e){layerSets=1}
    var loopStart = layerSets;
    var layerListFirst = getLayerSetsData();  
    var r = new ActionReference();
    r.putProperty(stringIDToTypeID("property"), stringIDToTypeID("targetLayersIndexes"));
    r.putEnumerated(stringIDToTypeID("document"), stringIDToTypeID("ordinal"), stringIDToTypeID("targetEnum"));

    var curList = executeActionGet(r).getList(stringIDToTypeID("targetLayersIndexes")); 
    var curLyrIdx = curList.getReference(0).getIndex() + loopStart;

    layerList.reverse();
    idxList.reverse();
    for(var i=0;i<idxList.length;i++){
        if(idxList[i] == curLyrIdx){
            var cLayerSelc = i}
            }

var dlg = new Window('dialog','Select Layer');
dlg.location = [500,100];
var dList = dlg.add('dropdownlist',undefined,layerList);
dList.selection = cLayerSelc;

dList.onChange = function(){
    selectLayerByIndex (idxList[parseInt(this.selection)],false)
    dlg.close()    
    //selectLayerByIndex (index, add)
    }

dlg.show()

function getLayerSetsData()
{
    //var count = 0;//set counter for multi-dimensional array
    var lyrSets = [];
    while (true)
    {
        ref = new ActionReference();
        ref.putIndex(charIDToTypeID('Lyr '), layerSets);
        try
            {var d1 = executeActionGet(ref)}
        catch (err){
            break;
            };

        var c2t = function (s){return app.charIDToTypeID(s);};
        var s2t = function (s){return app.stringIDToTypeID(s);};
        var lyrSet = {};

        lyrSet.name = d1.getString(c2t("Nm  "));   
        lyrSet.type = d1.getInteger(s2t("layerKind"));
        if(lyrSet.type !=13){
            idxList.push(layerSets)
            layerList.push(lyrSet.name);
            }
        layerSets++;
    }; 
    //return lyrSets;
};

function selectLayerByIndex(index, add) {
  add = (add == undefined) ? add = false : add;
  var ref = new ActionReference();
  ref.putIndex(charIDToTypeID("Lyr "), index);
  var desc = new ActionDescriptor();
  desc.putReference(charIDToTypeID("null"), ref);
  desc.putBoolean(charIDToTypeID("MkVs"), false);
  try {
    executeAction(charIDToTypeID("slct"), desc, DialogModes.NO);
  } catch (e) {}
};