Welcome to the Guild!
1) What it needs is partly dependent on where it is. Seashore, maybe river's edge, there'll be fishmongers. Midforest, not so much. On a main road, maybe an inn, but not a necessity. If isolated, needs to be more self-sufficient -- do you want to have wagonloads of grain going to the river-town a mile or two away, to mill flour? Some shopkeepers might be week-long; a market might be one day a week. That latter in particular if your town is a hub for nearby hamlets and villages to come buy supplies and swap news. Does your town have a specialty? Not every burg would have glassmakers, big-time weavers, a boatwright or a tannery, but some would.
2) In what order? You're probably shooting for 'plausible' instead of 'historically correct' -- there's far less record of town and village layout from half a millennium ago, than cities. Given a bit of thought how your town grew, whatever would have made sense to 150 years of locals will make sense to the reader - especially if you have it mapped. There you'll get the benefit of the "it's documented so it must be real" effect :-). If your folks are so organized as to have a common grazing area, for instance, then that commons might need to be central, and protected, if you're in woods with carnivores. Or if all is peace and tranquility it could be out of the way, at town's edge. Imagine how smart your townfolks are -- are there public wells usefully sited? Or does everybody dip buckets of water out of the river just downstream of the stable (now you need a bugger graveyard...).
3) I know what you mean about hard to search for. I bet most of what you've turned up has been tourist info on how a bunch of medieval towns are NOW. Try googling "recreated medieval town" or "preserved medieval town". "Medieval town map" seems to pull up some useful stuff. Hey, in Sweden you probably have more of that available than where I live - all MY local medieval towns were Cherokee or Chickasaw Indian villages :-). What I can see from a look at a few pages of results is a vast difference among sizes of towns - do you have a good idea how many people inhabit yours?
A thought - try using the image-specific search when googling "medieval town map" .... if nothing else you'll use up a whole evening perusing the interesting results (akkk - I know I will, now! )
You have a delightful enterprise in mind -- an opportunity to teach as well as entertain. Thanks for trying to 'get it right' instead of just blindly winging it!