My oil burning pig. Pics too!

As Sire said - they come with the seals in many cases (factory and aftermarket). The seal goes on until the guice contacts the inside "top" of the seal. Take a measurement on a new seal if you need to know exactly how far but mine always just stop. If you force it, ot hit too hard, they'll just break.
Worn guides can be felt by removing the seal and opening the valve ti mid-lift and trying to wiggle it in the direction of the path it follows as it opens and clsoes. They can also be measured, which is what I do if I think there's a problem but I can't feel any slop in the first test. Bronze guides don't use a lot of clearance so measuring may be the only way to get a real picture of them. Just measure the ID of them in the direction of travel.
A positive type seal will not stop oil from going down a bad guide because the valve stem is allowed to move too much in that case. Umbrella seals can be stuck on anything and provide some sealing. Positive seals only work with limited lateral valve stem movement.
The PCV won;t stop your issue. Because it's not made to dispose of excess oil... But it will go a long way to helping the seals do their job. They are designed to seal liquid oil under no pressure. Yours is pushing liquidf oil under pressure down the guides. At least i think so...