The best advice is that you should call a licensed Heating, Ventilation and Air Conditioning (HVAC) technician to ask for his opinion because it all depends on the make, the model number and the air quality in your locality.
once a week is recommended
You should get your floor machines serviced once every other year. They require regular upkeep in order to last a very long time.
Annually. If it`s fueled with oil absolutely annually.
Your fuel tanks are built to last the lifetime of your vehicle. They should only need to be serviced if they are damaged in an accident, or if some contaminant has been added to the tank.
Both Fox and Rockshox has a range of models, and which is "best" will be more dependent on which model you get rather than which brand you get. Oil-air shocks needs servicing fairly often if you ride hard, so if that's what you're getting, get the brand of shock that you can get serviced easily.
once a year, or 15,000km whichever comes first.
If it works properly, never.
Inspect at least once a year, base service on what you see.
HVAC should be serviced about twice a year. I prefer service just before summer so I'm not left in the heat and just before winter so I'm not left in the cold.
I have found that the filter should be changed around 90K in normal use and 60K in severe conditions. Toyota Tech.
That will depend on how the vehicle is used and what the manufacture recommends. It could be as soon as every 20,000 miles or as long as 100,000+