in need of some advice for flow in 3ds

Hello, first of all sorry for not posting any photos, I am at work, but my mind spins around this for quite some time, so thought I'd ask since most things are very straightforward.

My questions concern 3ds modeling.

a) In case of an arc, how can you properly extrude edges in a vertical direction?

b) In case you want to add extra detail in a 12-sided cylinder for example, how can you add extra edges in-between without ruining the roundness of the cylinder? I mean, if you start with an incorrent number of sides or in case you don't need extra polys, can't you fix it later?

c) Is there a way to 'expand' an edge polygon using it's sides? Like extruding in the same direction as if it was longer.

Any points to tutorials would help heaps. Thanks for your time, in case I am not clear enough I will try to post photos asap!

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