Welcome to the forum!
I'm not an expert of freshwater fish but its been my experience that the Danios in my brothers tank tended to pester the guppies from time to time. A lot of the folks around here have some experience with them and can provide better advice.
I personally would advise against using a fish to cycle, but I understand the urge to see something in the tank. The only thing I would suggest if you proceed with a fish cycle is that you keep a spare 10 gallon around empty except with water to move him into if he starts showing signs of distress.
Preserving the balance of your tank is the most important thing here and cycling is an important stage for your tanks life cycle. It should be fine to keep a hardy fish in the tank during this process, but I
stress the word
fish (singular). Putting too many fish in to begin is only asking for trouble and dooming the fish.
You will do well if you have patience and take things in moderation. We're here to help so don't be afraid to ask a 'stupid' question. There are no stupid questions for a beginner, just remember that. (and everyone else too!

)
Aaron