Plastic machining accuracy & surface finish considerations

Hi,

I am reviewing a circular part, made by "polypropelene, homopolymer, natural".Which is having o-ring groove for vacuum sealing and oring groove finishing requirement is 16Ra Circular Lay. Most of the dimensions are in 3 decimal(inch)accuracy and +/-.005(for general feature location), +/-.003 for oring groove width.

1) i would like to know whether i can achieve 16Ra in plastic material ?. (i cant go with polishing process on the component because it result cross contamination on the part.)

2) what is the maximum finishing value can achieve by machining on plastic ?

3) what is the dimensional tolerance, we have to go for position the feature from edges, center to center of holes ?

4) what are all the secondary operations i can do on plastics to achieve the finishing value?

please share some information about this.
Thanks
Vimal VV