Pat,
You don't say what day of the week you are checking in, but that mostly determines the buildings you will be in (although I am starting to hear that even this rule gets bent occasionally). I think you already have the resort map, but the online version is here:
https://www.vistana.com/destinations/sheraton-vistana-resort/map.
IF you are booked into a 1BR, you will be Lakes or Cascades as already stated. Lakes building six might get a little noise from I-4 but there is a fair buffer there compared to the back buildings in Fountains II. I would suggest you just go to Google maps earth view and zoom into the resort, you can easily see the distances involved. If you are checking in on Sunday, there is a chance you could be put in Lakes 6. However, the Sunday check-ins in Cascades are worse as two of the Sunday buildings front 535, and two front the main road through the resort. BTW the map indicates Friday in Red, Saturday in Blue, and Sunday in Green.
I would not call either of these sections "the quietest" in the resort. Lakes and Cascades are the newest phases, and have a much higher unit density than the older phases. With higher density comes higher noise; you are in a mid-rise building with elevators and lots of people coming and going. By far the quietest section of the resort is Falls, nestled in the back corner of the South side of the resort with spacious 2BR villas in 2 story buildings, it is a very serene atmosphere.
As far requests go, yes Vistana Resort accepts all requests from all types of guests through their Diamond Lane access.
https://owner.vistana.com/services/diamond.jsp?propertyId=01 A couple of things with Diamond Lane; they will do their best to meet reasonable requests, and generally are able to do so, but it does get more difficult if you are travelling at peak season and the resort is truly full. Also, they do accept requests for assignment to a room outside your category (no upgrades from a 1BR to a 2BR). Also note that the definition of full at Vistana is not like a hotel. With many units held as deeded weeks (like ours), the resort cannot access those units even if the owner is a no show. If I don't arrive until Wed of my week, my own unit must be waiting for me. So sometimes when they say they are full, they look anything but full because of all the absentee owners.
Vistana Resort is our home resort and we have stayed about 8 times now. Between trade-backs and guests, I have had a chance to stay in or see many of the unit types at the resort. They are all very nice and well kept with top flight finishes, and the resort offers great amenities. It is the standard we hold all the other resorts we have stayed at up to, and most are wanting. Enjoy your stay!