WELCOME !!!
Sounds like you found a GREAT Town Car!! You'll have to post some pictures for us regulars so we can be more intimate
Enjoy your Town Car !! 
Here's some answers:
The engine light indicates a fault. It can be read at most big name auto parts stores. They'll connect a reader, and print out a ticket that tells you what the faults are. In some cases they'll recommend a repair but their not mechanics so take that with a grain of salt. You can post your fault codes on the forums for some honest recommendations. In some cases the fuel filler cap was left loose, that'll set off that 'service soon' lamp too.
Well, you're up to 42k miles, so you've past the MASSIVE 30k mile service recommendations. If they were done as prescribed you should be good to go with just a tire inspection, possible rotation, and an oil/filter change.
A note re: your misfire. Our transmissions are finicky, they require 30/40k service. Most of us also add a friction modifier to the older Dextron but your's, with the new Dextron V shouldn't need an additive. Wont hurt though.
Lubegard is what most of us use, IF desired. For earlier years it's required.
I'm mentioning this because, we get a 'shudder' or what can be described as a series of quick repeated slips that can be mistaken for a misfire, and it normally happens at around 40k miles and at the 2nd to 3rd up-shift or 40 mph. The regular transmission services at recommended intervals will make your transmission last for decades, and keep it trouble free.
Here's the 30k Miles Recommendations: (
page 13, here )
( You can also get the Owners Manual here ), ( Factory Service Manual here )
30,000 miles
Cars, Minivans, Light Trucks, Sport Utilities, Vans, 4x4, Natural Gas, Propane, and Diesel Vehicles
O Change engine oil and replace oil filter
O Inspect brake pads/shoes/rotors/drums, brake lines & hoses, and parking brake system
O Inspect engine cooling system and hoses
O Inspect exhaust system and heat shields
O Inspect steering linkage, suspension, and if equipped driveshaft and ball joints
O Inspect tires for wear and rotate
O Replace engine air filter
O Replace fuel filter*
O Replace cabin air filter, if equipped
O Inspect accessory drive belt(s) (Villager and Escort)
O Change automatic transmission/transaxle fluid on all vehicles equipped with AX4S, 4F50N, 4R70W,4R100, 4F27E. Inspect automatic transmission fluid level on all other vehicles, if equipped with dipstick. Consult your dealer for your particular requirements.
O Replace climate-controlled seat filters (Navigator, if equipped)
*If vehicle is registered in California, the California Air Resources Board has determined that the failure to perform this
maintenance item will not nullify the emission warranty or limit recall liability prior to the completion of the vehicle’s useful
life. We, however, urge that all recommended maintenance services be performed at the indicated intervals and the
maintenance be recorded.