Thanks again for the well-wishes and tips - the enthusiasm and humor of this community is part of what drew us in! That, and this kinda nifty car...
Saturday FedEx brought us our salvage ignition lock housing, so I pulled the key cylinder, did the sticky key fix, and got it installed. Surprising how hard it is in Chicagoland to find a company to re-key the cylinder; many say they "don't work on that car". We could use the salvage key and swap it into our fob for starting, and just keep the old key for the door/glovebox/airbag, but that seems cheesy. Holding on reinstalling the lower dash until I can get the lock re-keyed.
Pulling and checking the #31 fuse for the lighter/glovebox light (was fine) seems to have solved the lighter power - now it's good on accessory & run key positions.
Did a quick check of the door switches for the always-on interior lighting problem - heard a click behind the headlight switch whenever either door was opened, so the switches are good. Need to check the actual relay at the headlight switch, or the output to the trunk security pump.
Found out why we had no heater blower - fuse #36 was missing. Thanks to the spares thoughtfully provided in the fusebox, plugged in a 40A and the blower started running right away...with the key off! This explains why the fuse was yanked. Can't seem to find my digital multimeter to check the controller, but the resistor pack is a likely culprit and Chinese down to $20 shipped on eBay, so ordered.
Of course, with the passenger dash tray already lowered for the resistor, the cabin air filter beckoned. Dang, that thing is substantial, and full of leaves and bugs. When my wife heard the $39 price of new (at needswings), she thought it sturdy enough to withstand a hosing and bleaching, and took charge of that refurbishment. Helps save the teenage wallet...I did notice cheaper alternatives on Amazon later. Looks like fuel and engine air filters are recommended at 60k, so we might take that maintenance step as well (but all of these CAI and Mercedes intake mods are awfully alluring). The Carfax that the seller had showed the first 15k as a lease, then the rest of the mileage up to 167k as one-owner, dealer-maintained, so we might be in a decent spot.
Best audio bang-for-buck capacitors installed - was fun having Max learn the basics of soldering. Base Infinity sounds pretty good now. But I feel air movement at the subs behind the seat without the pressure of bass, so we'll have to investigate those foam surrounds.
Valvoline/Zerex G 05 coolant I found at the O'reilly near us, but it doesn't match the blue I see in the expansion tank. Nonetheless, we'll be rolling again soon.