One thing to note as the OP mentioned twr and gnd were combined so that the OP probably heard the T/O clearance while on gnd control. So if the RJ is still on the taxiway behind you, don't jump out ahead of him, you made the right move there.

One thing that drives me nuts is people calling ready for takeoff from the runup pad while stationary. If you're not at the hold-short line or use "ready at the end" you're not for takeoff.