To the OP , i see you said you buy from the auction house , it is not really needed but if you do only buy if it is cheap and a very good upgrade , i only go for agility upgrades and whatever else i get is a bonus , on my main server all the decent upgrades are usually very expensive and most times are around 30g+ so my lower hunters have some armour sometimes 15 levels below them , but i always try to get a decent bow/gun/crossbow as we are ranged dps so i believe in hitting as hard as possible no matter what armour i have on.
You can if you wanted level with only quested items right to level 80 and without buying anything, and would have enough gold as you level to buy all your mounts and only visit the auction house to sell what drops you have found , although i do buy armour and weapons if they are cheap to make it a little easier , its your choice but something to think about.
As an example my first hunter brought and made a lot of stuff between 50-60 and as soon as i went to outland replaced almost everything with either quest rewards or drops on my first day there , i am finding the new area is almost the same but have not done much exploring or questing there yet so i am guessing much of my rubbish gear will be replaced very soon.