2. English is enough for working in IT. Live gets a lot easier if you know German in German-speaking Switzerland, French in western Switzerland or Italian in Tessin (southern Switzerland)
3. I searched online and was approached by Hays. Then I had three interviews with three offers and took the best fit.
4. I moved alone but my girlfriend already lived here which made it easier of course
5. 10 years in total, 1.5 years as project manager in an agency, 8 years in a big utilities company. Had a side business for web development since 2009.
Looking back I would say getting that job was even easier than finding a new job in Germany. Developers are searched for so you can easily apply to open vacancies even if they do not explicitly search for foreigners. I can recommend jobs.ch as a source for jobs.
I think you've possibly misunderstood what you have been told by your friends - you don't need to show your bank balance to a landlord. However, it is true that you have to apply with a dossier of files as specified by the agency or landlord and you can expect these to contain a copy of your contract (and so your salary) and also a statement from the local debt/claims agency (best English approximation I can think of for "office de poursuites/Betreibungs- und Konkursämtern") attesting to the fact you do not have any outstanding claims against you. It is unlikely as a foreigner that you will.
However the essence of what you were told is correct - there is a lot of demand for apartments in Geneva and Zürich. The occupancy rate is well over 99%. It is less a case of searching for the flat you like and applying than applying for many apartments and hoping you are chosen by the landlord.
[1] If you have a work visa you already should have a AHV number. [2] If you would work as a "freelancer" for only one customer it will look like your "employer" just want to avoid to pay into the social system. [3] Your sole proprietorship company should be profitable after about 5 years.