depends on your base level of fitness at the moment. If it's not the best, start with short (ie less than 3 miles) and build it up from there. As for pace, again it's down to your fitness etc.
Best advice is to go to a specialist running shop to get your running style checked in order to get the right shoes for you. There's no point in running in neutral shoes if you're as flat footed as I am, You'll only end up injuring yourself or your runs ending up painful and therefore you'll be loathe to go out.
Try this website to help plan your routes and distances