I built something like that. I'm practically the only one that built and regularly rides a drop bar road bike though (for 4+ years now).

Biggest problem: Nothing will fit on your handlebars. Drop bars have a larger diameter than flat bars, so you can't bolt anything on. I use an on/off throttle (a doorbell actually) as I just use the motor as a high speed boost - its low torque high rpm, so the on/off works fine for me.

How big a tire can you use? Bigger the better. I think 35-40mm would be ideal. You can go skinnier, but of course you'll need higher pressure and bumps are harder at higher speed (and your bike is heavier).

That motor doesn't list its RPM - you really should know that so you know what you are building. I think that is critical.