There are at least two different 4-4-2's with the 8602 number, but judging from your description, it sounds like you have the one from the early 2000s.
1) You'll be fine operating on 12v DC. The 103 electronic reverse unit inside the loco will function equally well on AC or DC. The only problem you'll run into is that your whistle tender will sound constantly on DC.
2) I THINK some versions of that later 8602 loco have a smoke on/off switch. If so, it's located on the opposite side of the chassis from the reverse unit switch that you've already discovered. If nothing is there, then no, there isn't any way to turn the smoke unit off short of disconnecting it inside.
While there are those that look down on these locos, your comments are exactly right -- they're smooth runners, good smokers, and represent a good value.
TRW
