For your question regarding section 3, you can use an EventHandler so that the boxes are evaluated when a particular key is pressed. For example:

CurrentValue[ SelectedNotebook[ ], { InputAliases, "qty" } ] = ToBoxes @
  EventHandler[
      Defer @ Quantity @ SelectionPlaceholder[ ],
      {
          "RightArrowKeyDown" :>
            Module[ { box, input, new },

                box = EvaluationBox[ ];
                input = First @ NotebookRead @ box;

                new = Quiet @ Check[ ToExpression[ input,
                                                   StandardForm,
                                                   ToBoxes
                                     ],
                                     input
                              ];

                NotebookWrite[ box, new ]
            ]
      }
  ]

With this, you can use the input alias qty to generate a Quantity template, but pressing the right arrow key will automatically evaluate the quantity in place (see attached video).

Edit: DynamicModule wasn't necessary

Attachments: