See this post on formatting the dates:https://stackoverflow.com/a/1056730/2033671
to get a date object in your case you can split the val and create a new date.
var date1 = $('.main-order-form input[name=start_date]').val().split(".");
date1 = new Date(date1[1] + "." + date1[0] + "." + date1[2]);
your second question, is a second question! Try some stuff out and ask when you get stuck