Weight is less of a consideration for an e-commuter. This makes a chro-moly (steel) bike a better candidate for a hub conversion because the rear dropouts on the frame or or front ones on the fork are better able to take the stress of a motor. For a middrive conversion alloy or steel are fine.

My first conversion started on an alloy bike. I posted a pic of the rear hub motor on it, prior to wiring, and was chastized for not having torque arms. I immediately changed it over to an older steel frame bike. Total weight with battery is 52 pounds, one of my heaver ebikes. I ride it and like it though.

Another consideration is whether your bike has space on the frame for mounting a battery. I have one bike which has a rack mount battery over the rear wheel. While it looks dorky, I have not found the 8 pound battery over the wheel to affect my regular riding, but a downtube battery is a probably better.