I know on most birds you can’t tell the difference in sexes, but what about Quaker Parrots ?

Quakers cannot be told apart by their plummage. Very few birds have distinctive markings that are 100% accurate by sex. Budgies have different colored ceres depending on gender (blue = male, brown = female). A few other species have definative markings, but most differences between parrot genders are not conclusive.

As far as talking, it is rumored that males favor talking more than females but this has not yet been proven. Both male and females can become aggressive, much moreso when left in pairs, and quaker parrots are notoriously tricky to keep hand-tamed.

If you want a bird that will keep you as it's favorite person, I advise adopting an older bird that has already gone through puberty. Young birds will bond to you as a baby does to a parent. As they grow up, instinct drives them to seek a mate outside of the family unit. This can and often does lead to your bird "rejecting" you. If you get a bird that has already gone through this stage, it will bond with you and the odds are negligible that it will reject you later on.

I wish you the best of luck, and continue to do your research!