iiiiiiiit depends, imo. on
A: what your goals are in your comic
and
B: your stamina and willingness to sacrifice for it.
if your primary goal is to make a super popular webcomic, you might be a little bit screwed. however, that shouldnt be your primary goal, because your primary goal should always be telling the story you want to tell, and telling it as well as you can. so while having a slow update schedule might deter some subscribers, you get to live your life AND create the story without sacrificing quality or you-time.
by stamina, i guess i mean how fast you can knock out a page, and if youre able to work on your comic after work. my work is long and hard (but luckily sporadic) so the weeks when i have work, i cannot draw my comic. too tired. that might be the case for you, in which case you should factor that into your schedule. it may also mean you have to sacrifice free time - maybe a lot of it, sometimes. its important to find a balance - because your wellbeing and enjoyment of life are more important - that might include choosing shorter, or less frequent updates, or maybe skimping a little on the process (black and white pages, maybe, or less detailed. there are lots of compromises you can make and thats totally up to you if you want to make any at all).
also, seconding everyones advice on having a buffer. have a buffer take your sweet ass time to make the first month or two month's worth of your comic, and then you get to take your sweet ass time a little more once you start posting. it means if you cant face drawing for a few weeks, youre still on schedule and far from running out of buffer. (although id say dont let the missed pages pile up beyond 3 or 4. if you do two pages a week, try to slip in a third, or half a page extra, each week when youre behind to slowly creep back on track)
that all said, i know lots of people that are doing their degrees, or work full time - some working long and hard hours - that have webcomics they cherish. its possible, and all about organisation 
and to answer your specific questions:
i can typically only get one page done in a day. thats maybe... eight hours? ten? sometimes i can squeeze in two, but that tends to include starting in the morning and ending in the early hours of next morning hehe
im shite at organising myself. but i thumbnail out all my pages months in advance, so when it comes to drawing them i have some idea what i was banging on about in my script. that makes getting started a lot easier. and i discipline myself to do two pages, every weekend, which is easy because i have no life.
i think most readersll understand someone having a life outside their comic. its pretty much the norm. if an update is late, or updates are sporadic, or you have to take a hiatus, just explain why. people will understand, and its a lot better hearing 'hey i really wanna keep up this comic but i have a Major Fucking Exam and cannot be doing that right now. be back soon!' than radio silence, which could mean youll just never update again. if you do go on hiatus, best to give people an idea of when youll be back. clarity is the source of patience.
it depends. some people just want you to get the story out so they can read it, others are very happy to wait for art they really love. if you do wanna shorten the way you make pages, its better to find shortcuts than drop quality - do black and white rather than colour, but do black and white well. or simplify your shading, but make that shading good. dont think of it so much as a drop in quality; very simple pages can be dynamic and gorgeous.
also, youre ultimately making your comic for yourself, and for the story. you want to do the story justice. if that means putting a great deal of effort and care into every page, then thats what it takes. would you be satisfied if you didnt?
