Birthday Buy?

[Studentoflife]

I'm turning 21 soon in approximately 10 days. Can not decide if I want to buy a YG day date or not. I love the watch and will definitely buy it on at a later date if not now.
On a daily basis, i sport a Tag Heuer Aquaracer and a Rolex Submariner and occasionally my fathers AP Royal Oak 18k.

All prices mentioned below are in CAD.

I pretty much have 5 questions.

- How much should I pay for a used daydate yg? My budget is under 15k for which i have seen many watches but should i buy one for less or should i buy one for 15k.

- Should i pay more for box and papers or should i get one without? The guy i will be buying from is a trusted dealer and friend in Toronto. The price for the one with papers is 17500

- The normal wrist size doesn't seem to fit me, so how much should i pay for an extra link? Inherently how much do they cost??

-Bark or no bark? I seem to like to bark as well as the non bark, without any information on bark i would have to buy the non bark. Is there anything special about bark why do other people consider it good or bad ?

- lastly, How much depreciation should I be looking to incur? My dealer /friend offered to buy the watch back at 10% less than what i paid for it a year after is this a good amount of depreciation or should i be expecting less or more?

all replies are appreciated and will be throughly read. Im really going to buy the watch either way. Just need some more justification and education before.