Looks like you settled al well.
The overnight in Frankfurt should not be a problem.
This hotel in Langen seems to be good if you arrive late and leave early. Langen is not very exiting, good for one night. Sheraton at FRA is nice but expensive .. as mentioned already.
If you stay longer in Frankfurt, you should consider taking the train (S-Bahn) to the city, however, don't stay near the main station (Hauptbahnhof).