Good choice ;-)
The Reaper forums a pretty friendly and helpful, so between that, video tutorials and your book you should be ok. If you're looking for additional reading I'd recommend this: http://www.amazon.co.uk/Mixing-Secre.../dp/0240815807 although I don't own it myself I have a lot of time for Mike Senior, he knows his chops recording wise and is quite a Reaper expert too (he also frequents the forums every now and again). He also writes the Reaper tips column for Sound on Sound - http://www.soundonsound.com/articles/Reaper.php