Id not worry about the oil seperator as yet, 1st things 1st. Many cars dont run one at all, just a catch tank, or just a pipe to the floor, no point getting complex and expensive for nowt.

And oil temps may well be an issue as you using piss thin oil but could well be perfectly fine on a decent thickness oil.
40 oil rather than 30, and 1way valves, THEN see what happens.

Like said, the valves alone cure it on many cars.

Hell, some cars wont even run at all if the crankcase can breath in, CVHs etc do that.