i usually have 100-150ish grams bark in 500ml sep funnel and it gets messy especially with the base only technique.  maybe compare with that.  teflon stopcocks are ok.  i dont see any deforming from the naptha or lye on mine.  my ph meter is red with a black probe, not sure what brand but any meter should be fine.  if you like math you could save on a buying a ph meter and just calculate an approximate Molarity of a lye solution and figure out the grams.    vaccuum funnel would come in handy if you have one