No experience with cargo bikes, but I regularly pull my kid on a trailer on my MTB. Total weight is probably 60lbs? for the trailer. Not a problem, even with some good hills in the area. If you're going to be riding flats, I'd say no problem. Just have a few cogs on hand to change according to the load weight.

Yes, gears will be easier and will most likely get you there faster. But if that's your main concern, why would you be in this forum to begin with?