if it can be AUTO-PILOT then who wouldn't want to do?
1. there's no way to auto-pilot it. the only way i can think of a site being auto-pilot (eg, no human intervention at all) is to rely on plugin to extract content from other place and put as post. which is point less.

2. a person can have many blogs, there's no rule or recommended period before or when one can only start a new blog.

3. yes. handling many blogs at once could hurt the quality, even for the experts BUT there are ways of doing it. see, i myself have many websites.
http://www.goldfries.com - me
http://www.goldfries.com/inperson - me
http://www.buurps.com - me + 3 other writers
http://www.htmy.org - me + er...... i can't remember how many writers. i think got 4 la.
http://www.mustgolah.com - someone else writes the content. i just do the site / maintenance

and that's beside running my own business PLUS a few more sites not yet unveiled.

Yeah.. That's what I heard from others the other day.
That's why I started different blog for different niche.

Hmm.. I am thinking of 1 thing..

"Is it possible that readers only subscribe to the specific
blog label only?"

What I mean is, for example if the readers subsrcibe to
my post labeled "health", they will only get notified
whenever I posted about "health"..

Is there any feature or way to do that?

yes. of course can.
but i think google analytics gives more detail report.

try to get updated with hot topic/news.
then make a post on your blog with rich-keywords related to the hot topic.
make them unique and interesting, if got photo or video are better.
then digg and stumble your post around the net.
that is what I do when I got 2millions hits on topic that I made less than 2 weeks.

Don't SU your own blog. SU will ban you. 

Haha ok means the key point is u must create multiple accounts to SU your own blog haha