Depends on the number of teeth on the back sprocket, the dummies. Dunno what speed you are looking at cruising at, but with my lame 36v setup, I ride about 25-27 mph, while the motor only is good for about 23-24 mph. So I'm pedaling in 58-14 gear 98% of the time. I do tend to downshift for an uphill start to 16 rear, or 18 rear sprocket, and then back up to the 14 cog once moving.
My controller is sensorless, but only needs a tiny push to roll forward. Half throttle keeps the motor stalling down starting up, and I start to pedal and push full throttle once going about 6 mph. I have the range, so I don't worry about blowing a few watts on starts. 72-14 might be a bit harder to get going . So you just motor till 15 mph, no big deal. It might tend to jump teeth on the rear 14 tooth though, mine does if I push too hard on a startup. It doesn't do this on the 16 tooth gear. It will be like a longer lever pulling on the chain. Fixie will help with that though, since you won't have slack in the chain, or just a stronger tensioner than a normal deriailur. I bet 72 front and about 20 to 24 rear will feel sweet. Aim for about 3 mph faster than the motors top cruising speed. It's just too hard to pedal a motor much more fast than it's top speed. Too much, and you'll leave the sweet spot and may as well just turn off the motor and pedal.