From what I can tell 8 planes at minimum were targeted. You have the 2 from Logan that hit WTC, the Dulles that hit Pentagon, Newark that went down in Somerset(one of the passengers said the terrorists said that they were going to destroy the Capitol). Now there was also a plane at Kennedy(?) that had mechanical troubles and didn't get off the ground, resulting in several Arabs on board getting angry and then leaving, now wanted by FBI. You had a boxcutter found on a Delta flight out of Boston that was grounded. Same on a Delta flight out of Atlanta to Brussels that was grounded. Finally, those two suspects with boxcutters pulled off the train in Ft. Worth were on a plane out of Newark bound for San Antonio that was grounded in St. Louis. So that adds up to 8 very likely hijack targets.
My guess is the Atlanta plane was likely headed either towards a DC area target(attack from a third southern approach) or perhaps CNN Center, as it has been stated that Atlanta was a target. San Antonio flight? Perhaps a Texas target for symbolism, since they hadn't acted before they were grounded in St. Louis. Boston Delta flight? Perhaps the third for the DC trifecta, Pentagon, Capitol, WH, but if Atlanta Delta was headed there, then perhaps TMI. TMI makes sense because the first strikes were designed primarily for symbolism and to instill panic, and a release with a wind from the west would affect nearly the entire Northeast Corridor. So TMI is a credible theory, but not for the Somerset flight.
Interesting...the day of the attacks, my brother was putting together a presentation for a customer at CNN World Headquarters in Atlanta. Then came the instructions to "evacuate the building immediately". He had no idea what had happened until he got in his car and turned on the radio. CNN World Headquarters makes a good target for a large plane full of fuel.
The question begs to be asked though, "Why would they take out an ally?"
A rumor I've heard is that the other planes were headed at places like the CDC and the Mayo Clinic. That would explain Atlanta, but I'm afraid way too many of these rumors are nowhere near true. All we know for sure is that 4 planes were or were going to be highjacked. The rest is pure speculation, and until the FBI verifies the items you mentioned, I can't give it any weight.