Hi Kirstyn,
Let's see if I can help with some of your questions:
Diamond Lane: submit the online form 2 weeks before your arrival date.
Lakes and Cascades are the only two villages that have buildings with elevators. Your Sunday check-in could find you assigned to Lakes, Cascades, Fountains I, Fountains II, Palms, Falls or Springs (but *should* exclude Spas and Courts). As the Fountains, Palms, Falls and Springs buildings are all stairs-only access to up the upper villas, be sure to note your mobility limitations on your Diamond Lane request.
Zimmies, the Marketplace and Cascades Grill are all on the south side of the resort (near to all sections except Lakes, Fountains and Fountains II). The north side of the resort, where Lakes and Fountains are located, feature the Tacky Tiki Bar and the Tacky Tiki Bar & Grill. Along the same vein, the Super Pool is on the south side of the resort while the Fountains pool is on the north. So regardless of where you are assigned, you should be close to at least one of the "main" pools (Cascades is the third main pool, plus there are 4 additional "smaller" pools with less extended hours).
"Away from highway noise" is most of the resort

. The only affected buildings will be those that border the 535 or the I4. Just be sure you note on your Diamond Lane form that you don't want a building that borders either of the highways.
Once you submit your Diamond Lane form, you will check in upon arrival directly with the resort (there's nothing more to be done online). Just head to the Welcome Center and they will take good care of you from there. They will give you a map of the resort, show you how to get to your specific villa, provide you with a resort activities schedule.
I am pretty sure the refillable tumblers are still available

. You can purchase the cups at the Tacky Tiki Bar, the Cascades Bar & Grill, and Zimmies (maybe the Marketplace too? but I'm not 100% sure about that).
There is no charge for the poolside cabanas, loungers or tables/umbrellas, and you cannot reserve them in advance. Use is on a first come, first served basis.
Let me know if you have any more questions, or if there's something I missed!