Collapse and expand

I don’t think it’s feasible to add script to the plugin because there are simply too many ways of applying expand/collapse, and everybody wants something slightly different! Some want click activation, some want hover; different icons or font glyphs, at the front or at the end; some want all open, some all closed, some partially open; some want a clicked sub to close all sub within it, others just want the clicked sub to close; etc, etc, etc. No matter how generic you try to make something like that there’s always someone who “needs” it to be different.
So, I think the answer is No. However, if you want a starting point for some script to apply yourself, you could try this? :

jQuery(function($){
  $('.widget_custom_menu_wizard').each(function(){
    $(this).find('ul ul').each(function(){
      var an = $('<a/>', {href:'#'})
        .addClass('cmw-expander')
        .html('<span>▲</span><span>▼</span>');
      an.css({marginRight:'0.5em',textDecoration:'none'})
        .find('span').eq(1).hide();
      an.on('click', function(){
        var d = $(this).data(),
            act = d.open===false?'slideUp':(d.open?'slideDown':'hide');
        $(this).siblings('ul')[act]();
        $(this).find('span').each(function(i){
          $(this)[!i === !d.open ? 'hide' : 'show']();
        });
        d.open = !d.open;
        return false;
      });
      $(this).parent().prepend(an);
    });
  }).find('.cmw-expander').trigger('click');
});

1. No, the code above will not work for hover … and if you are giving any consider to touch device usage then you might want to reconsider the use of hover anyway? The code above adds an anchor element to each item that has a submenu, and puts a click handler on that anchor (to open/close the submenu). The code is intended to be a starting point, not a definitive solution, because, for instance, placement/styling of the anchor may not suit all people/themes.
If you need to apply hover, then the added anchor would not be needed, and you would be adding hover (mouseenter/mouseleave) handlers directly to the items that have submenus, and you would need to have a set strategy for what gets expanded/collapsed when.
2. Once again, there are a number of ways of applying the code. If you have something like the CSS & JavaScript Toolbox plugin then you could paste the code into it, ensure that it runs after jQuery is loaded, and you’re set. Otherwise you could paste the code into a file of its own, then load that file into either the header or footer of every page (ensuring that jQuery is loaded first). Or you could simply paste the code directly into the header or footer (if you theme provides separate files for them).
If you do anything with your theme, I would recommend using a child theme (if you don’t already have one) because then you would not lose the changes when the theme gets updated.
If you are not used to editing theme files, then I would recommend using something like the CSS & JavaScript Toolbox plugin.

Simple answer : Yes, of course it is.

Is it simple to do? Depends : If all you want to do is close any item already open at the same level as the one now being opened, then you could just scan parent’s siblings for the relevant data setting and trigger a click. However, what about that open item’s open descendants? Should they also be closed? Or should they remain open? Also, scanning siblings for a data setting is more expensive than filtering siblings for a class, so depending on the number of items in your menu, it might be better to switch to using classes to indicate “open-or-closed” instead of data.

Am I going to do it for you? Hmmm … prob’ly not.

This thread, 4th post, point (2) … ?