You can slow down the Quicktime videos and study the moves. The moves described there are a bit more advanced but they are worded very well so that everyone should understand them. If going even wider, which is an advantage to you on the rear more so than the front, go for the XL version of the Rhyno. In the end, much of a wheels strength comes from the skill used in building it and keeping the rim true, something that is very important in trials. First off, the main reason to go for a smaller frame size is standover clearance when you're off the pedals, and for the ability to lower the seat down low.
Many people go for the smallest frame they can before the toptube gets too short.
Frame material is a more a personal preference. Aluminum is more common yet a bit stiff and steel is less common and makes for a softer ride. There are many, many bikes out there. Trials specific and bordering on competition-only are brands such as Monty, Megamo, Crescent, Koxx, Kule Komponents, and Brisa to name a few. While more all around bikes that can ne used for trials freeriding and competing are from Norco, Planet-X, Pashley, Identiti, Santa Cruz, Heavy Tools, Giant, Cannondale, Trek, Schwinn, and Ellsworth to only name a few.