Lisa,
I see where you got your map. I would recommend you go to the website
www.WillCad.org. When you get there to go to "WDW" then "Disney World Maps", then scroll down and click on "Value Resorts". That map is higher resolution, and you will see that the building room numbers start with numbers corresponding to the building number.
All the rooms have four digit numbers, with the first number being the building number (with building 10 starting with "0"), the second number is the floor, and then the room is the last two numbers.
As for check-in, it is good for anyone visiting a Walt Disney World resort. There is a separate page for someone who books through a third party (like a travel agent), but you should be fine. All you need to do is go to
www.MyDisneyVacation.com. There you can indicate preferences, and do all the same things you would do normally checking in at the actual resort.
The real bonus here is that when you get to the resort, you are already checked in. You go to a special table and pick up your packet of keys, tickets, etc., and you are done!
Have a magical vacation!