2. a well maintained bicycle is very reliable, even if it is older
3. yeah, it is like walking. get a rain coat when your forecast says it might rain.
4. my advice get a hub dynamo to power your lights, never worry about charged batteries again. flash mode is not a good idea, also illegal in some places. helmets are overrated and are essentially victim blaming. But I get where is this coming from, instead of building a safe infrastructure the cities put the responsibility to be safe on the bicycle rider.
5. get a better sattle, never really had an issue.
6. very much depends on the place, in my town I'm as fast as a car on many daily routes, simply because I can use more direct routes.
7. what kind of bicycle are you using? everyday bicycles shouldn't do that, a good bicycle let's you ride w/o backpain. maybe your bicycle is too small or too big for you, they are not a one size fits all kind of thing.
It is not about becoming a "biker" or "cyclist" it is about that a bicycle is a good mode of everyday transportation and a very much less harmful one for cities. Not just in the Netherlands.