Yes.  If you're pool mining, it needs to go to your wallet first, and then to bittrex.  If you're solo mining, it will be in your wallet automatically, so you can just send them to the exchange from there.

The only thing to know about autosell is that it dumps onto any waiting buy orders.  It's good for speed, but it means you don't necessarily get the best price.  (It's good for those of us trying to acquire more nxs cheaply, of course.  Patience is rewarded, and impatience costs you a little bit. :-).  But from a mining perspective, it's nice because everything becomes fully automated.

Dont mine nxs direct to bittrex account it wont work.

You could, but most people recommend against storing large amounts of coin at an exchange wallet.  There's no reason to think Bittrex will have problems, but exchanges are often targets for hacking because of the large amounts of money involved.  Small amounts, no problem.

bittrex has an autosell feature.  https://bittrex.com/Lab/AutoSell

It doesn't automatically send you the BTC out of your account, but it does the conversion immediately.

for now by use this exchange manually
https://www.bittrex.com/Market/Index?MarketName=BTC-NXS
a automated conversion service that include NXS isnt known to me yet
but will be very likely happen in the next months too