How about the oxidation caused by adding dry hops? Is that real and avoidable for a simple homebrewer?
sure it is real - whether it is noticeable in its impact for you is up to your experience. I have had some IPAs display slight oxidation cues - but I was never able to definitively say it was from dryhops - it could easily have been sloppy racking practices. I've since been vigilant about flushing my kegs with CO2 always, and being sure to purge headspace anytime I open the keg.
to your second question - one method to minimize this is to add your dryhops to your keg or secondary carboy/bucket, flush the vessel with CO2 and then rack from primary on top of these hops.
the other method mentioned in the article is to presoak the dryhops in a small amount of boiled and chilled water and add the entire mixture to the secondary. I can't vouch for this method, only relaying the message.