Smoke, etc in dummy engine

I suspect most any fan driven smoke unit that you can find mounting for will work.  You'll want one with the 5V regulator for the fan as well.  I'm assuming you're thinking of the MiniCommander EX for this application?

You probably won't want a smoke unit that is used with the regulator circuit that seems popular with more modern locomotives, but rather one that has the resistor suitable for running from 12V which the MiniCommander will be putting out.  The 6 or 8 ohm resistor in some smoke units is more current than you'll want on the MiniCommander smoke output.

Good thoughts. Also, how does the Legacy vary the smoke output...a triac controlled output from the 18vac?

Well, to vary the smoke output, you probably aren't going to do that seamlessly with the MiniCommander.  You could kludge something up with the MiniCommander ACC model, but it would be separately addressed as an accessory and not as an engine.

Also, if you're planning on running this in an MU with a Legacy locomotive, you'll probably have to run in TMCC mode.  Although it's technically possible to do, I don't think the MiniCommander will recognize Legacy commands as it is currently designed.  That would be an interesting experiment, or perhaps a question for ERR.

I'm assuming you want the lights and couplers to act normally like they would in an MU configuration, right?

Hadn't thought about that. I just figured I could just run a dummy behind the Legacy U33C, but turn on some smoke and maybe marker lights...operate a coupler. Who has fan driven smoke units for sale complete?

I just tried my Speeder with a MiniCommander 2 installed, and it doesn't recognize Legacy commands, so I think you'll have to adjust your thinking to reflect that fact.  I suspect that the MiniCommander EX is the same, though it would be worth a chat with ERR to be sure.

If you can find a Legacy dummy like the Lionel 6-28295 that I have, it comes with the Legacy board, couplers, lights, and the Legacy smoke unit.  You could transplant all of that into your locomotive for about the price of all the parts you're looking at.  I bought my dummy for $100 a while back, I believe it was on the OGR sale board.

Of course, not all the Legacy dummies have all the features, so you'd have to find one that has all the stuff you want.  It's one way to get Legacy compatibility.

When I bought my Legacy PRR U28C, I just bought both cab numbers powered, it's like a "super" dummy.

Fan driven smoke units show up on eBay and in the OGR sale forum pretty regularly.