I was just in keys over Thanksgiving. A lot of new construction since IRMA hit town. Key Colony Beach got whacked pretty good. Did not go much past Marathon this time. KW too crowded touristy for me. A cruise ship hits the town and its game on. It will be better in late April but easter is late this year, so it won't be a ghost town.
PBIflyer has good recommendations.
Things I would do on the way down:
Dinner:
Mrs. Mac's the original, not #2 (key Largo Bayside) Great food eclectic atmosphere.
Lazy Days (Islamorada Oceanside). Good food great ocean views.

Stop at Loralie for sunset as PBI says it a great place.
Stop at keys fisheries in Marathon and walk up the stairs and got to the bar/raw bar
Cocktails at the Cheeca Lodge. (Oceanside) Its where I prefer to stay but its not old school.
Or Havana Jacks on Key Colony Beach. Brand new, thanks to Irma. (Oceanside)
Alabama Jacks on the way in is nice but I have not been there since the storm.
No Name Pub on Big Pine Key. Cool odd place off the beaten path. (That is where I usually make my U-turn and head back east anymore. Been to KW 20 times.)

Lodging I usually stay at Cheeca in the middle keys or either of the two Marriotts in Key Largo. The Hilton is under renovations. But for a good old school place, I heard the Casa Morada (bayside Islamorada)
Drop Anchor is a very clean old school place (Oceanside MM 85). Have friends that stay there.
GUV 1976 is right, fly back to Miami.

That's all I can think of now.