Yeah sorry I'll provide my hardware here later ... Thanks.It's hard for me to provide advice without knowing something about your hardware.
1) With that premise, to reduce render times - as other have already said - you have to delete (or make invisible to the camera) everything that is not visible in the frame, for example ceilings or walls if you are rendering an indoor scene. Also, make invisible the limbs that are covered with clothing (ex. men's trousers) and shoes: ith helps to lower the resources needed to elaborate textures.
2) It's feasible, provided that you want to learn how to use blender's rendering engine(s): DAZ to Blender bridge.
3) Again, it depends on your hardware. Ah: always always, always keep your video card's drivers updated.
We managed to install octane after a lot of suffering, today I will try ...