I'm in the same boat as you Tom. I'm a newbie with limited climbing experience, but I've done lots of summertime summit scrambles, mostly within Mt. Rainier NP. I recently checked out a book from the library called 75 scrambles in Washington (published by the Mountaineers I believe). Most of them are class 2 with some occasional class 3 moves. I don't have it with me right now, but I believe it listed Mt. Ellinor (Hood Canal area of the Olympics) and Mt. Wow (southwest corner of Mt. Rainier NP) as being good spring scrambles. Hope this helps and good luck!
I wouldn't worry about hiring a guide. You should have plenty of time to get into good physical shape as well as read up on hiking and snow travel to be completely competent on your own. Camp Muir is a non-technical (but physically exhausting) snow hike so I wouldn't get hung up on reading Freedom of the Hills if you never plan to do any technical climbing. A good website for information on Rainier climbing, including conditions for the Camp Muir route, is www.mountrainierclimbing.blogspot.com. It is not an official NPS site but it is maintained by the lead climbing ranger at MORA. Good luck!