1) How long can I expect my 5 lb CO2 cylinder to last at a rate of about 1
bubble/sec, 24 hrs/day.

As of today its 5 months. I dont see any pressure change and hope for one
more month. Mine 2 bubble/sec

2) What are people's favorite brands/sources for controllers.

http://www.dlink.org/aqua/CO2.html

3) Is there an inexpensive but reliable controller out there that I should
consider?

See the link above.

4) Are the solenoids reliable, or are they failure prone?

I dont use any.

5) How much of a hassle is controller calibration, and how often do you
have to do it? Are some easier to calibrate/maintain than others?

NONE.

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Thank You

Dominic
http://www.dlink.org/aqua