Greetings Bob C.!
Glad I could offer some help. Some final thoughts....If your ends are nine feet, you should not have any trouble implementing a wide radius curve. However, as I mentioned in an article you can see in The Academy, you might want to use a tunnel to hide a tight radius curve. Why would you want to even consider a tight radius curve anywhere? To give space elsewhere. Perhaps you want a yard on one end. Build it, then install a tight curve to the side for a return loop on the main, and hide it with a hill or a raised tier covered with buildings.
Isn't imagineering fantastic? Endless possibilities!
An 18" curve looks horrible to the eye, yet most conventional equipment will take it. Though toylike in appearance when doing so, AHM/IHC/Rivarossi full length passenger cars will take an 18" curve. If I'm not mistaken, the Rivarossi Berkshire and Hudson will negotiate such a curve also. The longer equipment needs a long drawbar attached to the coupler to achieve this feat, such as the IHC passenger cars come equipped with. 85 foot auto parts cars will derail, as their couplers do not have the same ability to swing radically enough to make the curve. Articulateds probably handle down to 18" as well, as the wheel sets are spaced on separate bogies. I have a Challenger which takes tight curves, but asthetically, I wouldn't want to see it on anything below 24".
As for DCC, can't help you there. At this point in history, I'm a DCCophobe
Primarily of the conversion cost for the fleet, topping a slew of other reasons. Perhaps I'll change my opinion in the future, or by force like when they switched from vinyl to CD's, leaving us no choice!
Good Luck!
George.