Inverter Tig machines might be different but using an older style machine I would sharpen the tungsten so the length of the taper was 2 1/2 times the diameter of the tungsten.
With 1/16 tungsten the cup orifice diameter can vary from 1/4" - 3/8" of an inch.
3/32 tungsten the cup orifice diameter is 3/8" to 7/16"
1/16 tungsten will handle the 140 amps of your machine so that might be the only size tungsten you will need unless you go down to the .040 tungsten for thin stuff. On mild steel the argon flow should be 8-10 cubic feet per hour, with the amperage anywhere from 100 to 170.
I have used .035 stainless wire for a lot of small or thin stuff on mild steel, and stainless steel.