I just went through this exact process. I’m also delivering by bike and decided to try an e-bike. I’m glad I built my own from a kit rather than buying off the shelf. I would recommend a geared rear hub motor kit with pedal assist and throttle, and separate battery(the biggest you can get). If you split up your day into lunch and dinner shifts, I think you can get away with a 20Ah battery assuming you don’t mind still pedaling with no motor down declines(slight ones where it’s pretty easy to do 18mph on your regular bike) and using a mix of motor and leg power for flats. I wouldn’t go less than 20Ah. If you want something where you don’t split the day and want to head out for 7hrs straight, you’ll need a bigger battery depending in how much you wanna pedal power it. Don’t get a direct drive motor. If you are riding along with no motor and hit the throttle for some help, it will actually resist you until you get the throttle to the right point where it’s doing Slightly more work than you. I think it would be perfectly fine and great for back and forth commuting of 10mi per day or something, but sucks for constant stop and go delivering all day. If I fight the motor too much my knees will actually start to get sore, which never happens on my regular bike. I’ll be investing in a geared hub motor. I don’t think an off the shelf bike would be good for delivering unless you’d prefer to throw down serious money on a nice bike with major milage rather than build a kit. I hope that helps coming from the perspective of likely the same needs from the bike.