Hey mate, so a few things about dry hopping and oxidation, also yeast.
Not being offensive, but it sounds like you are a relatively new brewer, if I have gotten this wrong please don't take this like I am telling you how to suck eggs!
Disclaimer: This is MY opinion. Everyone does things differently. Take what you think works, leave what you think doesn't. It's about what works for you, as you're brewing beer that YOU like to drink.
Yeast: There is no advantage to moving your fermentation for beer into a secondary. Controversial to some, but the act of racking from primary to a secondary fermenter is just an increased risk for infection, oxidation and loss of beer. Yeast will generally not undergo autolysis (mass die off, kind of like drinking the coolaid) for many months. The fear of moving your fermentation off the yeast cake to avoid 'off flavours' has long been negated.
Yeast will also not do anything to the hops unless you are hopping during peak fermentation. This process is known as 'bio transformation' and the jury is still out on whether it positively effects ALL hops, but from what I have found I much prefer a single dry hop addition during high krausen (peak fermentation) and that's it. If you have almost reached FG, your chance of bio transformation on the hops is minimal.
Oxidation: Oxidising your beer is a big risk when racking to any vessel. The only way to do it safely is through a no-oxygen transfer, usually from a sealed pressure fermenter into a keg that has been purged of all oxygen. To simply rack from one to another will introduce oxygen. Essentially it's only a risk once fermentation is really underway, as the presence of alcohol will accelerate the oxidation process. That's why you oxygenate prior to pitching yeast and then leave it be. Some fermentations benefit from introducing oxygen during fermentation, Mead being one of them but not beer.
Dry hopping: I already covered bio transformation under yeast, so if you're looking to dry hop then I would do it when you have about 3 days left before cold crash and packaging. Be aware, that big dry hop additions will increase the risk of 'gushers' if you are bottling, as the suspended hop matter can provide nucleation points for gushing, as well as other factors (i'm not an expert on why hops cause gushing)
The general consensus for dry hopping has been discussed ad nauseum on multiple forums, but generally you can go 'naked' and just throw em in. That's what I do. The second option is to use a hop sock (or nylon stocking) that's at least 2x the size of the hops you add, so when they get wet they can swell up. Weight it down with some marbles or other sanitary weight. Sanitise the hop sock and weights, pop it in and then you can remove it before packaging. This is probably what I would do if i'm bottling.
You will introduce VERY LITTLE oxygen by opening the fermenter lid. It's not like oxygen will just go gushing into the fermenter like the scene from a movie when a plane door opens. You just open it, sprinkle them im (or plop the sock in) and close the lid.
I'm sure people with more knowledge than me can correct anything wrong i've stated or add more.
