Will being a Mangaka take up all my time?
It depends on which magazine you write for, for starters. If you write for a once-a-month magazine (like Ribbon), you will only need to write about 30 pages per month (a little more than a page per day). This includes furoku (color drawings you draw outside your actual manga that are turned into merchandise), and color pictures for the covers of your tankoubon (if your manga is animated, you will also need to spend some time with that, too)… But if you’re just a normal Mangaka for Ribbon, your time will not be eaten up. (Some Mangaka even had a 9 to 5 job while they were starting out. Yoshizumi Wataru and Sakura Momoko were both secretaries during their first couple tankoubon ^_^)
If you write for a magazine that publishes twice a month (like Shocomi), you will need to produce 60 pages per month. (about 3 pages per day) this is a little tougher, but still not too bad if you budget your time, have good assistants, and don’t waste time with video games ^_-.
Where do Mangaka work?
Usually in their own homes. Sometimes they might rent office space (if they don’t live alone). They tend to move to Tokyo, as this is where the magazines are located, but some live in other areas of Japan and fax/mail in their stories. Business with the editors and other staff is usually done over the phone.
How do I get assistants?
However you want ^_^. Mizuto Aqua set up an ad in Shocomi and in her Milk Crown tankoubon, asking for assistants, some advertise in their tankoubon in their freetalk space, and others just employ their family members ^^; (Fujii Mihona’s assistants are her mother and brother ^_-)
When will I get to publish my first artbook?
…Maybe never ^^; Only the Mangaka who are really considered good "artists" will have their color pictures published in artbook-form. Popularity of the series also dictates whether or not there will be an artbook.