I think you have gotten some great advice here.
I think the potty training will be an issue. Just because an 8-week-old puppy can hold its bladder for 3 hours, doesn't mean it will voluntarily. 3 hours is probably a maximum, you would feel discomfort in your bladder long before you've reached your breaking point, right?
I am lucky enough to take my puppy to work with me. Until he was about 14 weeks old, I took him outside to go potty 10-13 times in a 24-hour period. If I didn't do that, he would have gone wherever he was and would never be housebroken. I used puppy pads for times when I wasn't sure if I'd be able to take him out before he needed to go for the first week or so, until I figured out his schedule.
Now he's 18 weeks old and it's once when we get up (7:30), once before work (9am), once before lunch (around 12:30), once in the afternoon (around 2 or 3), once before dinner (around 6), and once or twice more before bedtime.
I can't imagine how things would be if I left him by himself for so long. I think you might have a much much easier time if you didn't get a puppy. I'm not sure where you live, but here in the US we have animal shelters and rescue organizations with millions of adult dogs waiting for a home. An adult dog can hold their bladder all day and would be less stress for you in general. You'd still need the neighbor to check in during the day, especially if you have to work late or something, but things would be a lot easier all around.
The allergy thing is interesting too. I got tested for allergies yesterday and found out I'm mildly allergic to dogs! Who knew? My allergies are livable unless I also have a cold. I think I might start an allergy thread to hear some more about these living with allergies ideas.
I guess I'm in a rambling mood today. Sorry for the long post!