I sent you a PM about Como. For the D&S I suggest that you ride in an open car and sit on the right side for the best views. The seats are all reserved. To help you with the timing I suggest that you only ride the train to Silverton and take the bus back. It's 4 hours to Silverton and the bus is only 1.5 hours back.
For the C&TS I ride from Chama to Osier and back. If you're lucky you will have a double header to Cumbres Pass.
Denver is a nice city but for me I would not waste my time there with the train opportunities. I suggest riding the Georgetown loop then driving to Breckenridge and then over Boreas Pass to Como, then down route 285 back to Denver.