IMO, Digitrax is best. It's expandable, versatile, very popular,
One thing you might want to look into is JMRI. It's a computer program that works with your DCC system so that you can adjust CV's, speed matching, lights, sound, and all the other functions on the computer. I've seen a few online tutorials and it seems to be better than trying to do everything through the throttle. A lot of people use an old laptop just to use for train layout related business.
You should also isolate a spur, or have a track on your workbench as a programming track. If you try to adjust a locomotive on your layout with a bunch of other DCC equipped locos, you could screw up their settings. Having a programming track means that you can safely isolate that one engine to adjust as you please.
As for running analog locomotives on DC. The club members have been using DC locos on our Digitrax system for years without any negative consequences. The only rule we follow is to not leave DC engines on an energized track for long periods of time. DCC has a similar waveform to AC current, so really we are running DC engines on a track that has AC-like signals embedded into the current. The only consequence I can think of is that the DC motors might have a shortened lifespan, but something else is bound to break before the motor.