The hill climb is the tough one. I would look at one of the geared hub motors, something skewed more towards torque than top end. Since it sounds like it will be a retrofit to a regular bike frame that pretty much rules out any sort of mid-drive. Stokemonkey or pushcart are great ideas but it's one more thing you have to haul around. Since you aren't coming down the hill I'd say regen is not a big plus for you. If you can plug in at work that will be a huge battery saver.
Assuming there are no traction issues on the hill climb, like a dirt road, you could go either front or rear hub motor, else rear may be better. I like the concept of battery on the back, motor on the front for weight distribution.
Since you will be bike racking it, I'd go for a Topeak-style removable bag for the battery so you don't have to lift the battery and the bike onto the rack. I guess these days theft is a concern for many so sometimes a bolted on battery is the only choice.
Anyway, my 2 cents, good luck.