It's an expensive item and you don't have much selling history so, although the buyer would have paid, Ebay might hold onto your money.

You would have to do some research to find a carrier that would cover the item for that amount and would include cover for damage in transit.  I am certain that it would be problematic for you to find a specialist courier, and very expensive for your buyer.

As far as I know, a sale to NI would not incur any taxes.

BUT, I would not consider posting such an item.

Even  if you stick to your guns and find a buyer who will collect, there is still the possibility that they could get it home and then start a return case.  At least you would be able to go and collect the item.  If you post, and the buyer opens a return, you would also be responsible for postage back to you.

Personally, I would say a firm 'no' to the NI buyer.

You won't get your money before posting it, and you are liable for any loss or damage during transit. 

Plus, if your buyer decides that it's not as described you have the difficult task of arranging and paying for the return of your item before your buyer can get a refund via eBay's Money Back Guarantee.

My advice - stick to collection in person only or add a shipping option that just includes UK mainland.