I've been doing light city cycling for 2 years now on my Brodie Section 7 http://www.brodiebikes.com/2010/bikes/section_7.php. I live car-free so I take public transit when I need to get between cities, and ride my bike for running errands/meeting friends within this city.
I've been pretty content with the maintenance-free nature of the bike and it suits my needs perfectly for a really light weekly biking average of 14 km per week.
I've been trying to undertake some recreational cycling on weekends with a friend in some parks in North Vancouver (Canada) which consist of either light trails or paved roads, but hills destroy me. I can't really practice on hills during weekdays because my city is completely flat, or I'll have to travel to a different city after the work day and practice at night.
I'm seeking advice on how to transition to using cycling for fitness:
(1) How often does one need to cycle to see any visible improvements in fitness?
(2) I know I need to practice first before I can deal with more varied terrain, but is my bike also a factor? I'm 110 pounds, 5'4 and female, which I guess makes my bike of 27 pounds + rack + fenders a bit of a tank. Should I look into a second bike?
(3) Got any other general tips for making the transition?
It's hard to say what my fitness level is. Due to living car-free, I walk a lot on a daily basis, and I hike probably 15 km a week for day trips. I think that covers everything. Thanks, your feedback is appreciated!