OK
-aerate when the wort is cold not hot
-wort holds more oxygen than water
-you cant over aerate with air but you can with oxygen - oxygen is a reactive chemical
-lots of different methods work, shaking, pouring between containers, racking via strainer - if you do it properly all of these will be sufficient.
-most of us who use oxygen actually have some welding equipment around so we already have an O2 tank. It is probably overkill for a 5 gallon brewer.
The next point is purely my vague opinion so take it as that:
It's probably OK to aerate the wort with yeast in it for the first 24 hours :horror:
There is nothing magical about the yeast being in the wort vs. the yeast being in the starter. Assuming that the yeast population is still growing its ok to add oxygen - once the yeast population has hit saturation then adding oxygen will lead to weird cogeners being produced. This opinion is a bias from my backround making wine, where must aeration during active fermentation is a standard technique.