Is keeping my nxt in my exchange account valid?

What if I but nxt from polo and keep it there? Do I receive ardor?

Also how does the snapshot system work? If I have 100 nxt starting July 14 and sell half after a week how much will I receive? Is it 50 ardors? 100+50/2= 50 ardors?

Also how long is this snapshot period? Is till the release of ardor? In this case might it not limit nxt transactions.

Thanks.

P.s I already own nxt but am intending to buy more.