Generally you want to use the standard HDTV format and pick the frame rate for your location. If you live in a PAL country choose 25 frames per second. In all other countries choose 29.97. Use the Presets in the Composition Panel.
If you see Custom in the Preset panel or you see anything but Square Pixels your composition is not standard. DO NOT use 24 fps for broadcast.
Check with the broadcaster for the delivery format. They are very picky. They are also very picky about color space, color levels, Audio levels and Audio Quality. It's much easier to get a commercial rejected than you know. You MUST follow their specifications or they will reject it. Broadcasters must maintain a very strict set of standards.
Also, if you are making a :30 second spot you should keep the audio to 28 seconds and if you are in the US you must use Drop-Frame timecode to assure yourself that the commercial will be the right length. The exact max and minimum audio standards will come from the broadcaster but 28 seconds will keep you save.
You'll also need to know about their Slate and countdown requirements. If you don't talk to them you are going to have a problem.
I would do the edit in Premiere Pro, use After Effects for the visual effects or composites and mix the audio in Adobe Audition. AE does not have sufficient audio tools to guarantee that you have "legal" audio.
BTW, if your broadcaster requests 720 for the frame size then you should still work in a full HDTV frame and just render your final product to their required format. This will save you a bunch of time later when someone wants a full HD version.
It is highly unlikely that you will be asked for a 4K product. If you do make sure you get the exact specifications from them for delivery. Just last year I delivered at least 10 different formats to broadcasters. I'll say it again, you have to ask them for their specifications.
Thx Mr. Rick for your explained reply, its very helpful & I am gonna to ask them to be in save side.