How many hours a week are you looking at putting in to this? Would be a fun job if you’re only looking for pocket money on top of other work. If I was doing this as my main line of work, I’d rather use a scooter or even a car - higher overheads tho.
So maybe 9 hours a day working time. That's not so bad for someone who actually enjoys riding a back (as I imagine you do). I actually considered doing this job myself a while back. What potential does your area have for deliveries? I've only seen one or two people out in Kawagoe so I guess not many people are doing it yet around here. Kawagoe is also pretty spread out so that might mean long trips to make deliveries and less pay per hour.
A guy I know who is normally a bike messenger who said he's been doing Uber Eats recently because the pay is so good. This is in central Tokyo, plus he's a bike messenger so knows how to save time in traffic.