I am sure you mean Aruba when you write "RUKUS" :)
ArubaOS do have support for WEP-128. You can refer to the Datasheet at below link:
http://www.arubanetworks.com/assets/ds/DS_AOS.pdf
From your queries:
- Why would you need a single channel throughout the site?
- You need to plan your network well for optimized roaming and Aruba does have very good support for roaming devices.
- For RF planning, I recommend to keep it for Aruba Controller. Aruba Controllers have a built-in feature called Adaptive Radio Management (ARM). It dynamically assigns channels to the registered access points based on RF conditions long performing many other tasks like controller Tx powers, band steering and so on.
Based on the number of Access Points per site, you can go for an instant or controller-based solution.