2 urgent questions about hair-particles

Most important i need to make something like 3d-cylinders out of the hair particles, but i can’t find anything to control something important like the thickness.

I also wonder if it is possible to add more than one particle system to one object or add
more vertex groups to one particle system - or do i have to split everything to different objects.

is there really nothing like a thickness?

ok i found the basic thickness in the strand material drop down menu,
but this is not really exactly what i need because it doesn’t look round enough and the maximum thickness is also not much - maybe someone knows how to make
3d meshes like a cylinder out of the hair particles - is this possible ?

You can change the thickness and shape (rounded or spiked) of a hair particle in the Strands settings (Material: F5 > Links & Pipeline panel > Strands). Note that these settings appear in the render, not in the 3D view.

You can add several particle systems on the same object.

If you want to use cylinders as hair, it’s possible: In the particles settings, Visualisation panel, select Object instead of Path. Type the name of your cylinder in the “OB:” entry.