0.075mm is currently probably the smallest trace width (by the way metric is the std units lest use them, try reading the IPC-7351 stuff, mainly relating to the grid sizes (0.05mm basic), most modern components are metric, as is everything else, lets bring PCB design into the 21st century please.) that can be easily manufactured, often seen now on impedance matched boards, 0.1mm track and gap is pretty common and has been for over a decade with BGA designs.
Via sizes depend on number of layers you are going through, had drilled down to 0.2mm finish.