Insearchof,
I would presume that the 2007 TM you are looking to purchase is a used unit (although some unsold coaches are still out there, I suppose...) We bought a used 2007 40-C TourMaster with the Mercedes engine about two years ago and are very pleased with the cost per performance/features of the coach.
The Mercedes engine is a good choice for economy versus performance trade-offs, we get about 8 to 9 MPG on most highway trips, depending on grades, winds and if towing or not. The transmission is great and the ride is smooth due to the air suspension. I have been considering adding the SuperSteer brand motion control units to the air suspension (auxiliary valving) to reduce the rocking on uneven driveway entries at low speed, but otherwise have absolutely no complaints. If this is your first large coach, you will learn to "plan much further ahead" while driving in terms of turning, braking, etc. We tow a 2005 Acura MDX which is an AWD SUV of about 5000 pounds -- no issues with the proportional air brake and mountain driving is not a big deal.
I had some non-warranty work done on my large slide -- other than that I have just been doing upgrades to my coach to personalize it and make it just what the wife and I want: better HDTV receivers in the main area and in the bedroom, storage organizers, upgraded faucets in the two vanity sinks and in the kitchen, upgraded carpet, dimming lights in the bath and over the dining table...things of that nature. Most are documented in threads on this forum, here are representative examples:
viewtopic.php?t=2249
viewtopic.php?t=2471
This forum is great for tapping into the combined knowledge of TourMaster owners -- I always get thoughtful answers to my question here!
Chuck