Hmm. No meaningful cycling experience. Never commuted. Training for triathlons - except for no biking. Oh, and no swimming. But other than that...

A bike shop employee has talked you into a shiny new bike that you can't even afford.

And you want strangers to tell you how to convince others that this is "right"?

Honestly, you need to listen to your father. Which it sounds like you're looking for a reason not to, which has nothing to do with bicycles.

To me, it seems like you can't really afford a bike _or_ a car.