I change rotary blades when it starts being difficult to cut. Because I'm a bad driver and run into the edges of rulers on occaision, some blades last longer than others.
I have a Fiskars handle and can put several kinds of blades in it. I buy whatever is cheap.
Smaller blades cut curves more easily than larger blades.
I avoid hand sewing, so I can't tell you much about needles. I'm sure some of ladies who do it will help you out.