Drilling out the oil drains to 10mm and relieving the drains is a good idea but I haven't done it. More important is the restrictors and the sump breathers so you are on the right track. Spend a little time reading this thread and you will see that the so-called "head drain" is a waste of time.
If your catch can has baffles inside it should be fine to vent it into your intake as I do. If there is too much oil vapour you will need a second, baffled catch can in that line or a proper oil/air separator. Catch can vented to atmosphere is illegal except on a track only car and on a street car you don't want those smells coming in through your ventilation system anyway.